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Thread: sink trap fundamentals

  1. #1

    Default sink trap fundamentals

    HI, I have a question about how the functionality of a trap changes by the difference in height of the input vs. the exit. Also is there a maximum water level height that can be in a trap. I am re-installing a garbage disposal on a replaced sink, since the the new sink is deeper the centerline of the discharge tube (horizontal part) is only 1/2" higher than the centerline of the drain pipe. , If I build a trap, what is the maximum alowable water height allowed by code if there is one, and is the effectiveness of the trap affected by the difference in heights of the input and exit? Thanks, Acercone

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    Water won't run uphill, so as long as the outlet of the p-trap can flow down to the drain in the wall it will work. It should have in the order of 1/4" per foot minimum. More is okay.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default trap

    As a practical matter it would be difficult to construct a trap with a level that is too little, just because of the fittings you would have to use. The more water in the trap due to a greater depth, the more possibility for the drain to run slower, so make it as short as possible.


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