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Thread: Can you tie lav drain into a toilet vent (wet vent)? W/SKETCH

  1. #1
    DIY Member kmuddzy's Avatar
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    Default Can you tie lav drain into a toilet vent (wet vent)? W/SKETCH

    Hi. A few questions (tried to change the title):

    Question 1)

    This question has nothing to do with the sketch and probably isn't that simple but here goes: Can I have the following drains all tie into a 30' long, horizontal 2inch "main" before this 2inch pipe connects to the 3" stack running to the basement? Or should I upsize to 3" where one of these ties in (which one)?

    In Order
    2" washing machine (farthest - 30' from 3" stack)
    1.5" laundry sink
    2" shower
    1.5" lav (middle distance - 15' from 3" stack)
    1.5" lav -2nd one
    1.5" tub (closest - 10' from 3" stack)

    Question 2)
    In the iso sketch below the 1.5" bathroom lav drain (yelllow) runs HORIZONTAL the whole length until the end where it drops down ( via 90) and then connects onto a 3"x 1.5" WYE (GREEN) via a 1/6. This green WYE connects to the vent top of the 3" Sani TEE from the toilet drain (purple). I gave the lav its own 1.5" vent. I assume this Green WYE becomes a wet vent in this setup if I understand wet vents correctly. Above this 3" green wet vent section I reduced it to a 2" dry vent to roof.

    Will this work? sorry - got double image and can't delete bottom one
    Name:  Lav wet vent off toilet.jpg
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    Last edited by kmuddzy; 01-26-2012 at 07:08 PM.

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    Member breplum's Avatar
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    Q.1 answer: UPC lists the total fixture units you describe as 10.5 f.u. and shows that you may have 16 f.u. on Vertical drainage piping and 8 f.u. on horizontal. So you can run the washing machine in 2" (3 f.u.) and laundry sink (1.5 f.u.) and shower (2 f.u.) and lavs are 1 f.u. apiece. so do the math and increase to 3" once you hit the max of 8.
    IMPORTANT NOTE: Tub trap and arm are ok in 1-1/2" but after the vent (within 3.5') it should be 2" pipe for the rest. also will be less prone to clogging.

    Q.2. looks pretty ok and should work fine. BTW, how did you draw that? IMHO it came out very easy to understand.

  3. #3
    DIY Member kmuddzy's Avatar
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    breplum,
    Thanks for the simple answer in Q1. I read about the f.u. requirements but I didn't fully get it.

    Re the sketch - I did that in AutoCad and did a screen capture to export the image. Since I'm new to plumbing I need to draw everything to understand/remember what I'm doing & the colors help me keep it all straight.

    Thanks again!!

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    Forum Admin, Expert Plumber Terry's Avatar
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    The lav trap arm can be up to 42" long and have one 90 degree bend.

    It can not turn down until it meets the stack or it no longer is considered vented.

    You're really going out of your way on this, instead of plumbing so that it works, you're trying to skimp on this. Once these pipes are in the wall, you're screwed.

  5. #5
    DIY Member kmuddzy's Avatar
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    Quote Originally Posted by Terry View Post
    The lav trap arm can be up to 42" long and have one 90 degree bend.

    It can not turn down until it meets the stack or it no longer is considered vented.

    You're really going out of your way on this, instead of plumbing so that it works, you're trying to skimp on this. Once these pipes are in the wall, you're screwed.
    Hi Terry - I respect your opinion so I'm hoping you didn't understand my drawing/explanation or else I am screwed! To clarify - the lav trap arm is horizontal to its own 1.5" vent only 24" away (and has one 60 degree fitting before the vent). The lav drain then continues horizontally until it turns down to join the 3" stack, which has its own 2" vent. The 1.5" and 2" vents will be joined in the attic.

    I cannot run the lav drain down since there aren't any walls underneath to take it to the basement, the joists all run the wrong way plus the space is finished below it so I cannot access the joists to drill if I wanted to.

    Does this clarify what I'm trying to do or do you still think I am skimping on this?

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    Forum Admin, Expert Plumber Terry's Avatar
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    I missed the vent with the blue dashed lines.

    But it was fun writing that. Not so fun to notice I missed the vent in the drawing.

  7. #7
    DIY Member kmuddzy's Avatar
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    thanks! no problem - just glad I can install it this way.

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