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    below slab floor drains (6 Posts)

  • AK_Todd AK_Todd @ 3:16 AM
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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?
  • Zman Zman @ 8:19 PM
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    Venting

    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.
  • Hilly Hilly @ 5:51 PM
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    in Canada..

    Up here a 3" P-Trap could be as far as 12' from its drain connection and not require a vent.
  • kcopp kcopp @ 8:09 PM
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  • Hilly Hilly @ 1:13 PM
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    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....
  • icesailor icesailor @ 8:15 AM
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    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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