Gurgling after using bathroom sinks - venting question! (pic attached)

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by TBrownMA, Aug 19, 2014.

  1. TBrownMA

    TBrownMA New Member

    Messages:
    9
    Location:
    Massachusetts
    I installed two pedestal sinks side-by-side in a bathroom, replacing a single bowl vanity. I plumbed it using 1.5" p-traps in a pretty typical way. Each sink's p-trap leads to a single 2" pipe running horizontal for about 3-6 feet (6' run for farther sink, 3' run for closer sink) to a vent that goes through the roof.

    With this setup, sink drainage seems OK but there is always a gurgling sound. I don't think there are any clog issues. I'm assuming the gurgling is because the horizontal run from the farther sink is like 6-7' from the vent pipe, and there should be a vent after the farther sink (see attached diagram).

    It's a ranch, so there is attic immediately above the bathroom. But the vent is cast iron in the attic, which would make it a pain to tap into. Would it be effective run a second vertical vent after the farther sink, and use an air admittance valve (AAV) in the attic (like 8 feet above the sink)? Would this solve the gurgling problem?

    I know AAVs aren't generally favored, but maybe it would be OK in this case since there's a roof-vent so close by?

    Thanks for any information! AAV attic.jpg
  2. Terry

    Terry Administrator Staff Member

    Messages:
    15,125
    Location:
    Bothell, Washington
    The sinks are not vented.
    That's why they drain quickly and suck the water out of the traps.
    The vent is meant as an air gap break in the siphon. that doesnt work if you try to vent below the trap.
  3. TBrownMA

    TBrownMA New Member

    Messages:
    9
    Location:
    Massachusetts
    Thanks for replying!

    Do you think the solution indicated in red on the diagram would work to vent the sinks?

    Or will I need to tap into the cast iron vent in the attic?
  4. Terry

    Terry Administrator Staff Member

    Messages:
    15,125
    Location:
    Bothell, Washington
    Last edited: Aug 19, 2014
  5. TBrownMA

    TBrownMA New Member

    Messages:
    9
    Location:
    Massachusetts
    I don't think there's enough room to put an AAV after the p-trap and before the wall. Should I put them in the wall immediately before the main horizontal drain pipe? I'll take a picture...
  6. Terry

    Terry Administrator Staff Member

    Messages:
    15,125
    Location:
    Bothell, Washington
    There is always a way to do it right. It may not be how you imagined it, but there is a way.
    If you put an AAV in a wall, it needs access to air. They do make wall boxes with grills.
  7. TBrownMA

    TBrownMA New Member

    Messages:
    9
    Location:
    Massachusetts
    IMG_20140819_162231854.jpg
    Here's a picture. I think I can make that work. How high up does it have to go above p trap? Higher than the sink's drain? I can probably get it up around 1" above level of sink drain, about 5" above the trap arm. Is that high enough?
    Last edited by a moderator: Aug 19, 2014
  8. Terry

    Terry Administrator Staff Member

    Messages:
    15,125
    Location:
    Bothell, Washington
    Higher is better, but you do what you can. It can be offset if needed too.
    Normally, in the wall you would have a santee with the vent above that. Do you know if that was plumbed in the wall without the venting going up?
    If its sucking the trap, maybe not. Though, if things are draining well, it may be the water going down the pipe quickly too.
  9. TBrownMA

    TBrownMA New Member

    Messages:
    9
    Location:
    Massachusetts
    Wanted to update readers with a picture and follow-up. Just in case anyone runs into a similar issue and is looking for guidance.

    Turns out it's a total PITA to put an air admittance valve between the p-trap and wall, but I managed to make it work. The real challenge was converting all the various sizes (p-trap, wall pipe, etc, of course all different diameters). Also very cramped for space, as the picture will reveal. Needed all sorts of connectors stacked together - or maybe Lowe's just doesn't have the best parts for the job. I used the Studor Mini-Vent, seems to work well. Had major tightening issues with the p-trap slip fittings to make them stop leaking, likely because I had such a cramped space to fit the p-trap that it's under a bit of tension.

    In any case, below is a picture of how it looks once I finished. The gurgling sound is gone, and the drainage is improved. I actually only needed to put the vent on one of the two sinks, it seems to be enough for both. I put it on the one that was making all the gurgling sounds. Now to patch up the wall and make it look nicer.

    [​IMG]
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