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below slab floor drains

Couple questions on floor drains. I've seen that a siphon can develop if your pipe extends too far past the p-trap without venting. I know there are lots of such drains without vents so is this really an issue or is there a special fix.

For those floor drains in the middle of the garage or in the mechanical room, do they need cleanouts? I ask because I've seen several drains with no cleanouts. I have seen drains with the a cleanout passage (that go to the other side of p-trap) in the side of the drain bowl. Other than one of these drains or a whole-house p-trap, what options do I have for small (2") floor drains clean-outs?


  • ZmanZman Posts: 3,344

    Drains in the middle of slabs are required to be vented. The vents branch off close to the trap and go to a nearby wall. There are commercial traps with cleanouts. Why do you need one? Zurn makes quite a few. Plumbing waste and vent is pretty involved. It is not something you learn quickly.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • HillyHilly Posts: 352
    in Canada..

    Up here a 3" P-Trap could be as far as 12' from its drain connection and not require a vent.
  • HillyHilly Posts: 352
    still needs vent

    That is a 2" drain which means that there will be a vent take off required within 8' of that in some form, be it individual, wet....
  • icesailoricesailor Posts: 7,265
    Trap to vent distances:

    In MA, a 2" trap outlet can't be more than 6' developed from a vent and 3" is 8'.

    Minimum drain size under a slab is 3" with short runs of 2" allowed.  You can "Wet Vent" a floor drain trap/drain with a sink drain, tied in closely to the trap where waste water from the sink will splash over into the FD trap so you won't need a trap re-sealer.

    If the trap is in a garage, it is supposed to rum through a oil and gasoline interceptor.
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