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Thread: Need Advice: Slow draining sink with no vent.

  1. #1

    Default Need Advice: Slow draining sink with no vent.

    I have a slop sink in my basement that has always drained slowly. Until recently I could never see what is in the picture (under the steps in a sealed crawl space). I cannot figure out how this drain is vented. The main stack that vents the bathroom (sink and tub) in the basement is a good 30' away. And there is no plumbing on this side of the house on the first or second floors. I assume it is just not vented.

    My question is can I put T and install the AAV where the red dot is? Or can I install a T and put it where the blue dot is? I have already checked my local plumbing codes and they do permit AAV's.


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  2. #2
    Master Plumber Redwood's Avatar
    Join Date
    Dec 2007


    Ideally you would have a through the roof vent.

    The lack of vent is not why its draining slow though.... You have a clog!

  3. #3
    Plumber jimbo's Avatar
    Join Date
    Aug 2004
    San Diego


    Your problem may not be the lack of vent, but rather a fairly long horizonatal arm with little to no slope

  4. #4
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default drain

    IF your problem is caused by the lack of a vent, which may not be true, then an AAV will do ABSOLUTELY NOTHING to cure it. The AAV will prevent siphoning AFTER the sink drains but cannot cure an airbound slow draining system.

  5. #5
    DIY Senior Member Mike Swearingen's Avatar
    Join Date
    Jan 2005
    On Albemarle Sound In Northeastern NC


    I would:
    A. treat that drain with a non-caustic, enzyme-based drain cleaner like DrainCare to help clean out any organic clogging. You run warm water down the drain, pour in the DrainCare, let it eat overnight, and then flush it down with hot water. I start the flushing with a kettle of boiling water. That should help clear most clogs.
    B. Install an AAV under the sink as high as possible.
    C. Cut that drain at the blue dot, snake the line as far as I could, and then lower the angle of that triple 90 to give it plenty of slope to help drainage. You might want to install a clean-out in lieu of the last 90.
    I'm not a pro plumber, just an old DIYer, but I solved a simliar problem by installing an AAV once.
    Good luck!


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