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Thread: additional trap

  1. #1

    Default additional trap

    I have a free-standing kitchen island which houses a smaller food-prep sink.
    Since venting vertically would have been impossible I decided to drop the 1.5" abs drain down through one of the hollowed out legs and place the trap below the floor.
    That way I can 'T' off after the trap to connect to a vent that travels up through to the attic inside an interior wall.
    Problem I see would be if any objects fall down the sink drain and become lodged between the sink and the trap (inside the hollow leg).
    Should I install another trap directly under the sink to catch fallen objects?
    Will this affect the performance of the second (main) sewer gas trap beneath the floor.

  2. #2
    DIY Senior Member finnegan's Avatar
    Join Date
    Aug 2005


    Your approach is creative, but it may not be the best option. Do a search for "island sink vent." You will come up with an island loop which is the traditional method of venting an island. An easier option is to use an air admittance valve (aav). You can run your 1.5" waste line right through to the rear of the sink base cabinet and attach your trap in a more traditional manner. Just do a search for air admittance valves and you should find all the information you need. Good luck.

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

    Default trap

    Two traps can cause a sewer gas problem, but will definitely impair the sink's drainage.

  4. #4

    Default added response

    Thanks Finnegan.
    I already searched and found many references to the island loop - traditional method of venting an island.
    However that would entail two 1.5" ABS runs to the basement - I only had one hollow leg in this island.
    I spoke to our local City Plumbing Inspector and he came up with the method of putting the trap in the basement.
    He also advised against the use of an air admittance valve since they are not permitted in this area.
    What I'm doing will pass the inspection .... my only fear is objects dropped into the sink have a 90 degree turn before they drop to the trap where they can be recovered.


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