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Thread: Bathroom sink drain slope / trap questions

  1. #1
    DIY Junior Member Tim Miller's Avatar
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    Aug 2013

    Default Bathroom sink drain slope / trap questions

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    Hello all,

    I'm finishing up a full bathroom renovation. It has been a seven-day-per-week job!

    I have a new bathroom vanity, and vessel sink. It sits much higher than the previous sink, and there is a bottom drawer in the vanity that hugs the sanitary tee.

    I believe that the `P` trap should be located in plane, more or less, with the sanitary connection at the wall. Unfortunately for me, this would require eliminating or modifying my bottom vanity drawer, which I would obviously rather not do.

    I would prefer to install the trap a little higher up, maybe even right at the sink drain, and make up piping as needed to the sanitary tee. Although this could result in creating a `S` trap, more or less. Or at the very least, a rather steep section of pipe between the trap and the sanitary tee.

    Any ideas on how to accomplish this without having to mess with that bottom drawer?

    I understand that S traps are no longer allowed by code in most cases, although in my brief amount of searching this morning, I have not seen too many horror stories about them. Just a theoretical tendency to jettison the water in the trap from time to time?

    Thanks in advance,

  2. #2
    Electrician Chris B.'s Avatar
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    Feb 2013
    Toronto, Ontario


    There is an alternative - open the wall.

  3. #3
    Test, Don't Guess! cacher_chick's Avatar
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    Jan 2008
    Land of Cheese


    Yep, you need to raise the sanitary tee inside the wall. If the weir of the trap is above the vent connection it will siphon the trap.

  4. #4
    Forum Admin, Expert Plumber Terry's Avatar
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    Aug 2004
    Bothell, Washington
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    Or............if you do raise the p-trap, you will then need to add an AAV to break the syphon when it drains.

    If I can get to those before the cabinet is installed, I like to cut into the wall and raise the santee.
    The other option, which I have done too, is notch the drawer.

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