Removing Old Tank

Used 5 year old tank can be a good investment, as long as the residue of tank bottom deposits are completely removed so you can see the condition of the inside of that tank. Even with just 5 years of condensation build up in the bottom of that tank, there can be the beginnings of some internal tank erosion, corrosion and deterioration.

As the installer of many oil tanks, I can assure you that lifting a fuel oil tank up from the basement can be somewhat difficult depending on the accessibility of the basement. Is there a Bilco® or equal basement door to the outside of the home? Do you need to bring it up thru the inside of the home?

• You will want to have the tank completely empty. or at least less than a gallon left.
• You will want to get four 2" plugs to seal the top openings with pipe dope not teflon tape.
• You will want to plug the 1/2" bottom with a plug, and not rely on the tank valve. They can break off if you drop the tank, and that can cause a real mess if that happens on the white carpet you need to walk across with that old tank out and the replacement tank in. (Ask me how I know this).
• You can use straps like the type used by furniture movers. 
• There are special straps with pipes attached to use as a cradle so you can stand on one end and your helper stands on the other end.  But I can no longer find them. So this may be. better option the get the same leverage

https://www.amazon.com/Forearm-Forklift-Appliances-Mattresses-L74995CN/dp/B008ASBLJI/ref%3Dsr_1_17?dib=eyJ2IjoiMSJ9.oQ_zvD8n648jSSG13MSgaN6EHdE-_JV6gdWfVro7q2E87nb8PaewE1QKJ2Cr9kELlCGOuvq-BPFiKENAa2WsbFo-TjRbT-U-IOtbWGzZNMyWduTs3DpCOE581SdY8K2SP4QJA25e_WGbTxBt5weTJlbFR6Hx8ACeZQjnQcmr0wYkz6ToEkhzASYCLd2mDkDxSg5W-yLsN-qqnkpjmKJebWZNQPv_6Mk06ArzrFfd898xp0n_qZ8w6XkVEk1NIfI1BI-JmhqatmVr5EcGFbOYog3Wr_y1jQcyO1TdxFP-fYo.XRMAU9gwD9hrVjJF7qpZ3XP1yKrnYzGxTJBsIXohnIo&dib_tag=se&keywords=lifting%2Bstraps&qid=1715960497&sr=8-17&th=1

And I have installed many tanks in my professional career with only two people. However installing a used tank brings to mind that fact that you should never put the oil from your old tank into your new tank. This is because no matter how careful you think you are, there is some nasty stuff in the old tank that you do not want in your new tank. Filtering while you are pumping out the old tank, Keeping the suction tube at least 4 inches above the bottom, and all the other suggestions that go aling with saving a few dollars on not throwing away your old oil, may cost you thousands in future repairs for your oil burner failing.

If you wan to save the old oil and burn it, then wait until you have no more than 1/4 of a tank.

• Pump that oil in a 55 Gallon drum and connect that drum to the fuel pump with a temporary fuel line.
• While you are using the old oil from the temporary fuel supply in the drum, install your replacement tank
• Get the replacement tank filled with fresh oil from a reputable fuel oil dealer.
• When you run out of oil from the temporary tank, reconnect the oil line from the new tank to the burner
• Change the oil filter cartridge and clean or replace the fuel pump strainer.
• Operate the fuel pump to prime the burner and let it flow for at least 1 minute after you get a clear, clean oil flow from the priming port or the high pressure port of the fuel pump.
• Once you have purged all the gunk from the new tank system thru the pump, (and you will still get some dirty colored oil from even the newest system components) then connect the high pressure line to the nozzle line of the burner.
• Now you can operate the burner.

If you want to hear my overkill method of keeping nozzles debris free, Just reply here and I will give you the down-low on how I have the fewest nozzle failure, as a result of the way I was taught to replace nozzles. I have been tols that i'm crazy for all the additional steps I take, But I also see professionals ask the question. "Has anyone had a problem with defective nozzles lately" and I have never had that issue in my 40+ years of oil burner service. Proper nozzle handling is the key to trouble free operation.

And I would take some additional steps to make sure your used replacement tank is going to be trouble free.

While the recommendations will certainly result in the cleanest possible used tank that one can obtain, the question that begs is "why bother"?

Everyone that runs a bottom feed tank must accept the inevitable accumulation of sludge at the bottom of the tank. The sludge, if the best filters available are maintained, never makes it to the nozzle. If one was so concerned with a bit of sludge in a 5 year old tank, you would need to explain how a 20 year old bottom feed tank runs perfectly fine.

I recently replaced a 275 flat tank that was 30 years old. The sludge in the bottom was far more than I would have expected. However, the nozzle didn't care!!

And, anyone that runs a top feed tank certainly has no need to bother with this extensive preparation!

And furthermore,  a bottom feed tank properly pitched towards the bottom opening will have less tank bottom deposits because every delivery will cause the tank bottom deposits to accumulate near the outlet. And less near the end away from the bottom opening. The fuel filter will then keep the tank bottom deposits from reaching the nozzle.

When you have a top feed, and do not have that constant fuel draining out the bottom, then you flush the tank each year to remove as much as you can,  

Or you can keep your fingers crossed.

A friend of mine purchased about 200 automatic delivery accounts and about 300 COD accounts from a competitor that did not want to do oil delivery any more.  Over the 50+ years that this company existed, they offered a service contract that paid for all the service calls at no charge, and included a heater cleaning.

We both found out the hard way that this company corrected a tank bottom deposit problem by installing top feed lines.  And as the problem became worse over time, the service men would just lift the fuel line a few inches off the bottom. And then a few more inches.   Almost ⅓ of the tanks have the fuel lines lifted as much as 9” from the bottom.  When the customers were entered into the purchasing company's automatic delivery system, the customers were running out of oil because they entered a 275 gallon tank in the tank size field. But the tanks were running out of oil with up to 50 gallons still in the tank.  The oil company asked me to find out what was happening. So I pulled the fuel lines and found the short dip tube lines. And also found inches of tank bottom deposits.  

Seems that the oil dealer did not want to lose an oil customer to the gas company, so there was a “no new oil tank” policy, at that company.  Go figure.

I have experienced many tank bottom deposit, or sludge problems over my 40+ years in the fuel oil, and oil burner service trade.  I only wish to share my experience, so others can try to learn the easy way.  Or keep your fingers crossed and perhaps, learn the hard way.

And what is interesting and contradictory in your second post is the first sentence where you cite that a bottom feed tank properly pitched toward the bottom opening will have less bottom deposits ………………

Then the new Company made the decision to correct BOTTOM FEED problems by installing top feed lines.

Why would anybody who understands that the BOTTOM FEED has less accumulated deposits go and install TOP FEED lines?

Again, something is clearly missing here. It could be that the entire issue is centered around OUTDOOR TOP FEED SINGLE PIPE systems (of which I have none). Or there is a lack of service to the filter(s) and/or the filter is inadequate.

That is the issue. Why will the nozzle "thank you later" for cleaning up all the possible sludge at the bottom of an old tank when the filter(s) should be doing that job! If there is a great concern about accumulated sludge, that is certainly going to happen over the next 10 years with the used tank or with a brand new tank. This is especially true in outdoor tanks. Either the filters take care of it or they don't. The problem, if you investigate it, is not the sludge in the tank. It's the lack of capability of the filter(s). They do the right job, the sludge is inconsequential.

I also am of the opinion that outside tanks demand a two pipe system for this exact reason. You have to circulate the oil to keep the sludge accumulation to a minimum. Naturally, changing the filter regularly is mandatory.

The community agreement on one pipe appears to be fraught with risk on an outdoor tank. My two pipe system with a used tank and old fuel is certainly a good example of the sludge accumulation being inconsequential and, therefore, the significant effort to dispose of all the old fuel and avoid a used tank is largely excessive.

I should note that the old fuel is only utilized down to the point where some discoloration of the fuel is evident in the suction line from the pump. At that point, the remainder must be discarded.

@LRCCBJ said: "I also am of the opinion that outside tanks demand a two pipe system for this exact reason. You have to circulate the oil to keep the sludge accumulation to a minimum."

You might change your mind on that rare colder than normal overnight when the viscosity of the 17 GPH flow rate of the pump gear set is more that the 3/8" tubing can handle. The viscosity of the oil at -10°F along with some condensation that gets stuck in the fuel line and freezes to partially restrict to flow of oil can easily cause the fuel pump to stop operating as a result of the enormous vacuum developed by the fuel pump. That restricted oil will actually stop flowing at a rate sufficient to maintain the oil pressure needed to operate and you will get a flame failure, then lock out on safety. And the fuel pump sings a high pitch song i like to call, "Don't Shut Me Down". It was a popular hit by a group called "The Bypass Plugs". They only perform in the cold northern climates around December, January, and February. I have gone to many of their concerts late at night during my career as a burner technician.

Have you ever looked in a fuel tank at midnight on a below zero evening with your flashlight". You can actually see the paraffin that has separated from the fuel, floating on the surface of the oil like blobs of cloudy looking solid pieces of wax. That is when you put your 5 gallon Jerry can in the basement and run a temporary fuel line so you can go back home and get some sleep.

@LRCCBJ A BTU is the amount of energy needed to raise one pound of water one degree.

Worst case scenario = full tank (or close to it) where there is almost 2000 pounds of oil at a cold temperature below my magic number of 17°F. Since the specific gravity of oil is about 0.874 then the conversion factor for the BTU definition would be about the amount of energy needed to change 1.14 pounds of oil one degree. So that would mean that to raise the fuel in the tank from say 10°F to 20°F you would need that oil to be heated with 17,400 BTU of energy. Unless there is about 500 feet of oil line coiled up in the basement sitting on top of that heater somewhere in the return piping to the tank, I don't see a 10°F temperature rise. in the fuel tank.

Do you have some type of evidence that the fuel tank actually is 10° warmer than a fuel tank with a 2 pipe system compared to a tank that is not using a 2 pipe system? I have 40 years of oil burner service experience, where I have been called to more than one "No Heat" call that is related to cold oil. More often than not, on a two pipe fuel pump system. I remember one particular overnight, where my son completed 7 no heat calls and I completed 12 No heat calls, and one other employee who was on call for emergency service completed 6 no heat calls that were directly related to cold oil. It may have been condensation freezing in the fuel line, it may have been gelling of the oil, it may have been a frozen oil filter on an outside tank. Every one of those no heat calls could have been avoided if the fuel line from the tank to the burner was installed with some basic understanding of how the physics of oil in a outdoor storage tank, reacts to cold temperatures.

Many of those customers were convinced to have fuel tank lines redesigned when the weather was warmer, so there was one fuel line within 3 inches from the bottom of the tank, that exited the top of the tank and had a downhill flow until it entered the interior of the home.  This way if there was any water or condensation in the fuel line, there would be no trap to keep water from settling outside where it could freeze. 

I am sure that the person that installed a fuel filter outside directly off of the fuel tank thought that it made sense to do this because there was no room for an oil filter inside the mobil home heater, or using a 2 line system made it easy to relight the burner when the tank ran out. The problem that these features solve, however, are also the reason the oil burner stops working when you most need it to work, at the coldest outdoor temperatures.

@LRCCBJ said "I also am of the opinion that outside tanks demand a two pipe system for this exact reason. You have to circulate the oil to keep the sludge accumulation to a minimum. Naturally, changing the filter regularly is mandatory."

I have been advocating this for years. I agree that the bottom feed indoor tant with the tank pitched toward the outlet is better than a level tank with a end feed that used to be popular.

My theory which no one likes is to use two pipe all the time indoor or outdoor tank (unless maybe if you have cold oil issues)

Two pipe with better oil circulation and good filters and you will build less sludge

Think of it this way,

New tank with a new deliver of oil ….starting off fresh.

Can you burn every drop of that first delivery with no sludge? Yes. We all know you can.

So obviously the sludge builds in the tank when the oil is just sitting there doing nothing.

Two pipe prevents this to some extent by keeping the oil moving and filtering it return clean oil to the tank.

And don't bother with and "return lines leak" I have been hearing that for years and not buying it.

Yea @LRCCBJ, but you may have a full tank on the coldest day of the year. Wouldn't you like to be able to use that oil?

As far as 20 feet of 10°F oil from a outdoor fuel tank routed thru 3/8" fuel line for 20 feet of heated basement at say 60°F, then returning to the tank in another 20 feet of 3/8" tubing, at a rate of 16 to 17 GPH, I still don't see the tank even with only 500 pounds of oil (about 1/4 tank) getting much warmer that 1°F.

…and to quote a famous man that is familiar to many on this forum. "For a difference to be a difference, it has to make a difference" …and at 10°F outdoor tank temperature, I don't see 11°F being a difference.

If you need more convincing, I will do the math of how a 3/8" pipe carrying a 10°F fluid with a specific gravity of 0.875 will absorb heat from a 60°F air space over a 40 ft span traveling at a rate of 16 GPH. I will wager you that the oil in the fuel line barely reaches 25°F let alone convert 500 pounds of oil to 20°F in the 40 minutes it may cycle per hour (40 minute per hour is based on the fact that most heating systems are oversized and the fact that once I got the burner up and running, it actually cycles on the high limit the entire time I was there See the PS below).

PS: I have actually been inside a basement at 11:00 PM with a customer and showed him the condensation that was forming on the fuel line turn to frost (like a suction line of a central air conditioner that is under-charged). The frost was most intense at the inlet of the basement wall and continued to the fuel pump, then eventually continued to the return line all the way to the basement wall where it exited. The entire time, with my vacuum gauge on the suction line the fuel pump started to labor and the whining noise gradually changer to a squealing noise, until the vacuum gauge reached 19"Hg. and the flame went out in the furnace.

I explained that I could get him operating with a tiger loop that I had on my truck. It took some convincing since it was overtime and the tiger loop flat rate price in my price book was not a cheep job. (the guy did not have a service agreement with me at the time, so no discount available). He purchased a service agreement from me that evening. He never has a no heat call again, all the way up to my retirement.

The fallacy of your argument is that you only consider 40 minutes as the time available to heat the fuel. Consider the fact that the fuel is under continuous heating for an unlimited time (at 10F) at the stated duty cycle of 40 minutes per hour. In 24 hours you are looking at 960 minutes of heating the fuel line. (Counter point: consider that you have 24 hours of cold air removing that 960 minutes of heat)

I Love This Reply, but still disagree.

Very good point @LRCCBJ, But I still don't see that a 16 GPH return flow of 20° fuel returning to the tank making any difference that matters when comparing a single pipe with no return flow.

On a typical colder than normal 24 hour period that might happen once every 5 years, (that is when I experience the most "cold oil service calls", so maybe not typical) I would expect that the sun ☀️ may have warmed up the tank 10° higher than the 19° high temperature by say 4:00PM. So now we have 150 gallons of fuel (your number) in the tank at an average temperature of 29° at 4 PM

By 4 AM the next day the low temperature is 8° and with no sun for 11 of those hours, to keep that oil warmer than the outdoor temperature, The gallons of oil loose lots of the heat energy to the surrounding air every hour. Now that oil has dropped to 18° in 12 hours. Of course that oil will not get to 8° because that mass will hold on to some of the heat from 12 hours ago, the way a cast iron radiator might stay warm longer than a copper baseboard radiator once the boiler stops circulating the heat.

Now, if we can agree that the oil in that tank on an 8° overnight low, is about 18° average temperature in the tank, then that will be our starting point for comparison. With a single pipe system there is no added heat from the 40 feet of copper in the 60° basement. so we have 18° oil and it is moving at 1 GPM thru the 3/8" fuel line.

Take that same home next door and it has a two pipe system and it had 150 gallons also. That will send the 18° oil to the basement in the 40 feet of 3/8" copper back to the tank. lets run the numbers:

• .00379 gallons per foot or 3/8" copper
• Total gallons of oil available for heat transfer 0.15 gallons at any given time (that's not even a pint 🍺)
• Entering temperature oil inside the tube 18°
• Temperature outside the tube 60°
• Total heat transferred based on the copper tubing thickness of 0.049"
• R valve of copper tubing 0.5 (based on an estimate of aluminum siding R value of 0.61 from building material values available online and lowering it because copper transfers heat better than Aluminum)
• Total surface of 40 ft of copper tube is just under 4 sq.ft.
• U value = reciprocal of R value
• Calculation Total heat transfer (Q) = U x surface area (A) x difference (∆T)
• Amount of heat transferred in 1 hour = 400 BTUh

Fig 1. Screen shot of a heat loss calculator

Even if we were to say that the heat transfer were greater based on a 17 GPH (or 0.28 GPM) flow rate that would cause oil to be able to transfer more heat to say 1600 BTUh (4 times the regular one hour rate, but this is not a practical application of the heat loss principle, but lets use it anyway)

Then 1600 BTU's (but really only 400) could be transferred to that tank every hour based on a heat transfer calculation of say water, with a specific of water at 1. There would be less actual transfer using oil with a specific gravity of 0.875

Now how do those numbers work with 150 gallons of oil. #2 heating oil weighs about 7.3 lbs. per gallon so that is a little over 1000 lbs. of oil. Every hour there is about 40 minutes of run time of the oil burner (because it is oversized and the radiators can not accept all the heat output of the burner even if the call for heat is more)

Now using that 1600 BTU per hour at one third (40 minutes or 66.666%) operating time that will give you just over 1000 BTUs per hour. You have about 1000 BTUs of warmer oil from the basement heat transfer, to mix with those 1000 lbs. of oil in the tank. And if you do the calculation with the 0.875 specific gravity multiplier, you ain't getting even one degree more heat in the tank.

Now even if that oil was being heated with that extra almost one degree every hour before 4: AM, the temperature drop would only allow less than one degree every hour to be added, while the outdoor temperature is taking away more than one, two or even three degree from the tank every hour.

Conclusion: Not gonna get 10° warmer, more like one degree warmer.

Have I made you think about it yet?

Yes, I thought about it carefully and I applaud you for the technical analysis.

I agree on the possibility of 1000 BTU/hr………..although it is probably less.

However:

"Now even if that oil was being heated with that extra almost one degree every hour before 4: AM, the temperature drop would only allow less than one degree every hour to be added, while the outdoor temperature is taking away more than one, two or even three degree from the tank every hour.

Conclusion: Not gonna get 10° warmer, more like one degree warmer".

You ignore the factor of time. Under steady state conditions of outdoor temperature, we agree that the tank will warm by 1F per hour. The open question is how fast it will fall per hour. Remember that you have 1000 lb. of liquid and a steel container between the outdoor temperature and the fuel. A 10 degree differential between the fuel and the outdoor will never lower the tank temperature by 1 degree per hour. My WAG is that you'd need at least 30F to accomplish that. Sure, you can go from 40F to 10F overnight but you'll never get the fuel down anywhere near 10F before the sun rises……….even without the added 1 degree/hr.

As I mentioned previously, there are other variables at play that determine whether or not the fuel gels and stops the flow on both the one pipe system and the two pipe system. I'd be curious how the one pipe system manages the tiny flow rate………..an invitation for fuel to gel in the 3/8 tube at .75 GPH…………and WITHOUT the benefit of the previously discussed 1F per hour contribution from inside the building!

BTW, it absolutely will climb by 10F over 10 hours under steady state conditions which we both agree are unlikely.

@EBEBRATT-Ed said:

"And don't bother with and "return lines leak" I have been hearing that for years and not buying it."

Well, once in a while they do, and when fuel oil leaks into the ground water, you can end up with a Superfund site. Why take the risk?

On this job:

https://forum.heatinghelp.com/discussion/148292/megasteaming-by-the-river

the underground tank was piped 2-line. We abandoned the return line and installed a TigerLoop on the supply. It has worked perfectly- no issues at all. An added advantage is that the filter doesn't get nearly as dirty.

"An added advantage is that the filter doesn't get nearly as dirty."

Unfortunately you have it backwards. You are leaving the accumulated sludge in the tank. The filter SHOULD get "dirty" if it is doing the job of cleaning the SYSTEM! You're ignoring the obvious.

@LRCCBJ said: "what would a one pipe system have done under the same exact conditions"?

I don't believe I avoided this. I addressed it on several customers, one of which I mentioned earlier. Here is another: I can say with certainty that the higher viscosity oil in that tank, on that 4th day of the cold snap flowed just fine with a one pipe from the tank, the firing rate of .85 GPH was slow enough that even molasses could flow thru that 3/8" line. I did not have a tiger loop at the time. (I don't think they were invented yet) but the 23 GPM of the old Sundstrand J Pump (now known as Suntec J pump) gear set was too much for that 3/8" line on that tank at that time.

So here is me addressing your statement. One pipe works better with cold oil than two pipe, the proof is in the actual repair. After that repair, there were no more No Heat Calls from cold oil the next few days of that cold snap, and in subsequent years.

I remember that winter like it was yesterday… or maybe like it was 38 years ago. Moving from Philadelphia to South Jersey was a transition from mostly middle income homeowners that I used to do service for, and what I learned on, to a lower income population that had oil heat. The permanent residents of Cape May County NJ were very different from those I remember on summer vacationing there. Also, Philadelphia has a code requirement that states there are no outside, above ground fuel tanks. So I never needed to deal with frozen fuel lines, Just fuel lines that were plugged with tank bottom deposits.

My first winter I remember blowing out frozen fuel lines to get oil to flow so the heater would operate for several customers, collecting my service call fee, then moving on to the next customer. The following night, the same customers called with the same problem. I honored the service visit with a warranty "No Charge" service to remove the blockage. The following evening, the same customers called with the same problem…. Fool me once…you know the rest. I needed to come up with a permanent fix for this problem.

• First, I needed to understand that water in a trapped fuel line was staying in the fuel line if there were traps in the fuel line that were exposed to the elements.
• Next I owned a push pull hand pump.
• Now I needed to get the tank treatment into the fuel line where it would do the most good.
• I made up a short suction hose that I would place in the bottle of HOT 4 in 1 and suck the chemical from the bottle and pump it directly into the tank bottom, where all the problems are.

This solved all the single line fuel tank freeze-up problems for the duration of the cold snap. I actually incorporated it into my price book as a Flat Rate repair that included the chemical and the labor to disconnect the fuel line and pump it thru. I also included a 10 day warranty on the fuel line not freezing up again. This was the repair that most customers purchased the first time around even though it was a little pricey, compared to just blowing out the clogged fuel line only. They would definitely purchase it the second time I was there. 🙂

On the two line system; I didn't need to address that one until a few years later. That was a different problem, during a 100 year low temperature event, that Al Roker called a polar vortex at the time. This problem manifested in high running vacuum when cold, but normal running vacuum during warmer temperatures. So changing to the one pipe system was the fix for that. But you needed to put the one pipe system in properly so not to have the freeze up problem I mentioned above . 

An in depth look at outside tanks and fuel gelling

https://noraweb.org/wp-content/uploads/2021/06/NORA-Freezer-Test-Report-6-21.pdf

All tanks are that dirty if nothing is done to mitigate the inevitable sludge/water in some way. Either it is constrained by the two pipe filter…………….or a treatment is utilized regularly…………or a top feed with ever increasing distance from the bottom…………..or it is an indoor tank. NOBODY gets away with your approach forever on an exterior one pipe.

I can clearly see that @LRCCBJ is not offering the surrender flag easily.

In my first winter at the NJ shore I ended up with the customers that would shop around, Not the customers that were long time loyal customers to the big three major players in the county. So my customers were the ones that did not want to pay full price for oil or repairs. That left me with lots of trailer owners or renters that had 2 pipe systems that were over 20 years old, and lots of one pipe systems that would freeze up whenever the outdoor temperature was below 17°F. That was my magic number. I may have mentioned that before.

So the first winter was a lot of one pipe systems where you can get water to stay in the low spot of a fuel line while oil passes thru the water to get to the fuel pump. That is because the flow rate was so slow.  Like 0.5 GPH here is a video of that issue.  Not sure if this link to a video is good (let me know)

https://photos.google.com/direct/AF1QipNcYmadDAQELUDYHAO9vGX2F31FuxBagZpZvixewuIBKiegRYvGe30xIPrabxddfQ

You can clearly see that When the burner starts, and pumps 0.50 GPH to the nozzle, the water in the clear tube is at a low point and the oil will push the water up a little then the water will let  the oil pass thru and the water will drop down the trap.

Now up to this time I would agree with @LRCCBJ because the two pipe systems were not having the problem, but another few years later I was schooled by mother nature again.

The third year I was there, that is when Al Roker let that polar vortex into New Jersey for over a week, the other customers with the two pipe systems were having the problem that was resolved by changing to one pipe. I never experienced oil that cold before. So I fixed it because by removing the bypass plug. I was able to confidently do the one pipe design because the previous experience with one pipe problems were easily solved with proper design and maintenance. 

Another point that I wish to verify is the fact that the fuel dealer that was lifting the fuel line from 4” to 9” off the bottom of the tank to avoid replacing or servicing the tank bottom deposits problem was the selling dealer.

I happen to work for the buying dealer and was called to the homes to solve a “no heat call” and would spend 30 to 60 minutes trying to get the oil to flow because there was still 9” of fuel in the tank.  After trying all my tricks, I went to the tank again and removed the suction line and that is how I found the problem. They were out of oil at 9”

After three similar problems, the buying fuel dealer asked the selling dealer if that was a common problem?  That is where the company policy of “no new tanks” was revealed.  (Who Does That?)

And your explanation of pumping 4 in 1 into the tank was probably misunderstood. That is my fault because I only made reference to the push pull pump and not the complete procedure. click the spoiler for the complete description of the service call.

To sumarize:

• One pipe allows water to stay in trapped fuel lines and freeze
• Three years later Solved jelling fuel with removing 2 pipe to slow the flow to the firing rate, so thick jelled oil can still flow
• The selling fuel dealer was the one that made the mistake of lifting the fuel line. I worked for the buying fuel dealer and had to learn the hard way that this was done by the selling dealer as a regular way to “FIX" a dirty tank problem.
• Pumping chemicals into the bottom of a tank through the fuel oil line until I heard the bubbles of air were there to agitate the chemical was the fix for any new customer that had the water freezing problem. (Not the jelling problem) I was looking for the water dispersant part of 4 in 1 to do the job NOW, not 3 days after I poured it in the top of the tank. 

I see that I may not have been clear on my explanation on some of the facts, stories, or experiences; based on your less that accurately restating them back to me.

I hope this clears up any confusion. My bad

@LRCCBJ said "Be assured, however, that the one pipe system has no magical capability to resist gelling in any way and probably suffers to a greater degree due to the extended time of the fuel in the 17F environment (assuming the tank is above 17F)."

Agree with above, but gelling fuel can move slowly thru a 3/8" fuel line but at can not move swiftly thru a fuel line. To explain it to a customer I use the McDonald's straw research. McDonald'd in the 1950s needed to offer a straw to their soft drink customers, but they found that the common paper straw that was less than 0.25" was collapsing when it was used with the milkshakes they served. Research was done to select the best straw for the task at hand. It turns out that a cold milkshake was more viscous than a cold Coke.(or root beer if you prefer) So the research discovered that a straw with an inside diameter of just over 0.26" was easy to draw a viscous milkshake thru without the straw collapsing. And plastic was better than paper for that job.

It just so happens that a 3/8" M copper tube is just over 0.25" ID, just a bit smaller that the straw. But when used to draw a milkshake thru 3/8" copper tube, like the straw, it needed the mouth to create more vacuum than the same copper tube would need for a Coke. (or Dr. Pepper if you prefer) So the ID of the McDonald's plastic straw was set at 0.2678"

How does that apply to this oil flow conversation you ask? Very cold can be as viscous ar a McDonald's milkshake. What does this have to do with fuel oil at temperatures? you may ask! Oil above say my magic number of 17°F will have a viscosity equal to a Coke (or a Diet Sprite if you prefer). But Oil that is sitting in an outdoor tank for an extended period of time, outside in the sub zero temperatures can Gell to a viscosity of molasses or a milkshake. And you should agree that the higher viscosity (Lower Temperature) fuel oil will go thru the straw or copper tube with the vacuum that your mouth can develop, but it can not flow as fast as 17 GPM of 23 GPM that a 2 pipe system might develop. There will be a much higher vacuum with the 17 GPM that there is with the 0.50 GPM in my antidotal example.

PS.

I offered the frozen water v. viscosity time line so you can see my learning curve. And so you can fully understand where my antidotal experience comes from. I was not born with oil in my veins, (although my father did carry a chip of coal in his head just above his right eye, for over 55 years… by the time the wound healed over that chip, it was in there to stay, Kids do the darndest things). I needed to learn by experience that a 2 pipe system had a specific use, and not to just install it everywhere so I didn't have to prime the fuel pump

@EdTheHeaterMan

whoa, whoa, whoa,

what did I say ? !