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Thread: basement bathroom drain venting

  1. #1
    DIY Junior Member teemstrohs's Avatar
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    Apr 2008

    Default basement bathroom drain venting

    i accidentially put this in the shower and bathtub section first. sorry. this seems more appropriate. thanks.

    ok i attempted to attach a plan drawing of the bathroom to make it easier to understand.

    the circle at the top is the main plumbing stack a 3" pipe (it switched to 4" after going under the slab and turning 90 degrees) that under the basement slab turns away from the planned bathroom wall at about a 45 degree angle.

    i have cut out the floor to expose the drain line and the area for the toilet.
    what i.m not totally sure on is how to vent this set up.

    2 things need to drain. the toilet and the lavatory sink.
    i plan on the toilet going and tying into the main drain at a 45. i wanted to bring the sink drain through the wall and turn 90 (down) and go into the toilet drain.

    how do i vent this?

    can i put a T in the sink drain so that when it goes down the vent for the sink and toilet go up? can they then turn over into the plumbing stack and be considered a wetvent. or can i put an AAV on a toilet vent? do i need to run the sink drain past the toilet vent and go all the way over to the main stack?

    any help would be much appreciated. thanks.
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  2. #2


    Ok, after your 3" 90 degree elbow in the floor for your toilet sweep install a 3" x 2" wye and run the drain from the lavatory to it and then vent the lavatory and the lav sink will be the wet vent for the toilet. Now you still need to vent the lav. sink. in my area using IPC we can use an air admitance valve.

    ps. you come up in the wall from the floor with the 2" drain for the lav. the drain needs to be 2" because it is also acting as the vent for the toilet.


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