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Thread: Upstairs Kitchen sink draining into basement kitchen sink

  1. #1
    DIY Junior Member DIYRENO's Avatar
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    Post Upstairs Kitchen sink draining into basement kitchen sink

    Hello,

    We are renovating our basement. There currently is a sink in the basement below the upstairs kitchen sink. When you drain the sink from the kitchen upstairs it drains into the sink below before draining. It has an AAV approx 4 inches from the P-Trap. If I removed the AAV and vent the basment sink directly would this solve my problem.
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    Any help is appreciated

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Default ddrain

    If the top drawing is what you intend to do, forget it. That "vent" would do nothing to solve the problem. The AAV cannot prevent positive pressure problems but that is not what you have. You have a plugged drain and until it is cleaned the problem will continue, with or without the AAV. one side note, a vent that turns sideways is not a "branch vent" it is a "horizontal section of a vent stack".
    Licensed residential and commercial plumber

  3. #3
    DIY Junior Member DIYRENO's Avatar
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    Default

    Thanks for the information. Yes the top was what I planned to do and the bottom is what is existing. We did snake the drain when we first moved into the house but did not have it done professionally so I guess that is the next step.

    Appreciate this site..

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    Two things: the AAV should be higher, and once a line becomes a drain, it can't be a vent. To properly vent the lower sink, you'd want to run a new vent up above the upper sink by at least 6" or 42" from the floor, whichever is higher. If the drain line isn't plugged or restricted, if the aav was a bit higher, that may pass code. You want the aav as high as possible if in a cabinet and still be able to remove it, or if possible, above the flood rim of the sink.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    In the Trades Tom Sawyer's Avatar
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    Well the top picture is just plain bad plumbing practice and adding the AAV may solve the problem but even with the bad plumbing practice the reason the sink is draining into the lav is because the drain below is plugged or partially plugged.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  6. #6
    Moderator & Master Plumber hj's Avatar
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    Default

    AAV manufacturers show the valve 6" above the drain line. Once the "vent becomes a drain", any "vent" is useless until the water drains out anyway.
    Licensed residential and commercial plumber

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