Is this correct?

Correctness:

I looked at this again. The below seem to apply.However: Plumbers don't pipe those things so most plumbers wouldn't understand about the fan/drain issue.

Maybe that's why you're asking about if the vent belongs between the drain and the P-Trap. That would break any syphon on the trap. As far as plumbing systems are concerned, it doesn't need a trap. The trap is in the indirect waste receptor where it enters the plumbing system.  



I can't see anything wrong with that. From a plumbing standpoint, it is correct. Assuming that the drain opening (inlet) inside the unit is open, and the water can flow out without disruption, there is a P-Trap with a vent on the down stream side, between the trap weir and where drain ends. If there is any sort of internal trap inside the unit, the drain is now "double trapped" and won't drain. You would need the vertical vent pipe moved to

Technically, it isn't plumbing until or unless the indirect waste from the appliance goes into the sanitary plumbing, into a properly wasted, trapped and vented indirect waste receptor with a air break.

I don't have a code book, but I seem to remember that whatever the size of the drain leaving the appliance, the drain is supposed to be one pipe size larger. IE: If the drain tapping is 3/4" IPS, the drain needs to be 1". So there is more air flowing through the drain pipe. The inspectors I dealt with didn't care unless it was for an icemaker or some other device. If that drains out on the ground outside through a outside wall, they didn't much care.

How To:

If you're asking me, I live in a 240 unit old carts place in Florida. They do things differently down here. Each and every unit has the AC unit inside and a 1" PVC drain run 25', under the concrete floor, that came out so low, that the "Trap" is upside down on the outside so the bugs can't crawl in (I guess). I had someone come and service the unit. I had them replaced the 1996 Ruud unit. The guy just came with his small Ridgid Home Depot shop vac, connected it outside and sucked the many gallons of water in the 25' trap, out. It was right nasty. I was told that a 25' length of 1" horizontal pipe with one end rising up 3 or more feet for a condensate drain, and an ellbow turning UP with another Ell turning Horizontally and another turning another turning down (an upside down P-Trap), on the other end, isn't a trap. It must be common because you can always tell when someone is comfortable with something you think is odd, it must not be to them. They want to extend the line away from the units after 30+ years. They bought 1" PVC running traps so the could have traps on the lines to keep insects from crawling in to the AC units up through the drain. I didn't score any points by pointing out that the only living creature that was going to crawl 25+ feet up that pipe was a fish. And that adding that running trap would make it double trapped. And not drain. Unless the head pressure of the water could overcome the trapped air between traps.



Any of you out there ever inadvertently double trapped a plumbing fixture? It didn't drain, did it.



So, if the question needs an answer, take the proper sized PVC cap and put it in that vent riser and suck away on the outside. It will work just like one of those Bouse House suck trucks that comes around and sucks up the honey from the job site Porta-Potty. Ma Nature hates a vacuum.



IMO.

Suction:

Usually, not a lot.

In the above example, if you cap the vent riser, and connected the shop vac to the drain at the bottom, it will suck it out as easily as it does from the top. And you don't have the cart the vacuum to the top floor.



IMO.