Can the J bend in a p-trap be installed "backwards"??? J-Bend Lo Inlet

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by zbdd2, Jul 9, 2009.

  1. zbdd2

    zbdd2 New Member

    Messages:
    2
    Location:
    Tennessee
    I am hooking up the drain lines under a relatively deep bowl sink. The installation includes a garbage disposal. In order to get the J-bend of the p-trap to meet the arm of the trap, I have to attach the long side of the J to the arm and the T that combines the disposer and the second bowl to the short side of the J. This is backwards to me but seems like it should work. Will it? Am I creating other problems?
  2. Terry Love

    Terry Love Plumber

    Messages:
    37
    Location:
    Bothell, WA
    It will work, it can raise the water level in the disposer though.

    Many kitchen remodels should have the drain at the wall lowered 3" if you are using a deep bowl kitchen sink.

    The last kitchen remodel I worked on, the contractor was going to just flip the p-trap.
    It would have left some water in the disposer all the time, if I hadn't caught it for the homeowner before the cabinets were installed.

    [​IMG]

    [​IMG]
    Last edited by a moderator: Apr 6, 2013
  3. zbdd2

    zbdd2 New Member

    Messages:
    2
    Location:
    Tennessee
    Lowering the rough in would have been the best thing to do but we had no idea what kitchen sink we would be using when that part of the project was done and the difference in the rough in never occurred to me. Disposer installation is new to me as well as how those affects things. The house was all but gutted and all of the galvanized supply and all of the cast iron dwv lines except for one run in a concrete slab were replaced. This is the last fixture that I have to finish the plumbing on and I feel fortunate that this is the biggest issue that I have come across. Live and learn.....

    Thanks for the info........
    Last edited: Jul 9, 2009
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,626
    Location:
    Cave Creek, Arizona
    trap

    Doing it will not change the level of the water in the disposer, as long as the pipe in the wall is not above the disposer's outlet. IF it is you MUST lower the pipe or you will have constant problems, not the least of which will be premature rusting of the disposer. One problem you will have is that the "outlet" of the trap has a very shallow insertion for the tailpiece so it will fall apart very easily if bumped or vibrated.
  5. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    Even Watts made this mistake on their website product pictures... :eek:


    [​IMG]

    Problem is like HJ said they fall apart easy and leak...
    Last edited by a moderator: Apr 30, 2014
  6. Terry

    Terry Administrator Staff Member

    Messages:
    15,001
    Location:
    Bothell, Washington
    I've never been able to get the plastic traps to stay together when reversed.
    I can sort of make it work with the chromed traps.

    But me, if I know there is going to be new cabinets, the first thing I check is draing height. Almost all new remodels are going with deep sinks.
    And that means lowering the drain while you have access to to the wall behind the cabinets.
  7. Terry

    Terry Administrator Staff Member

    Messages:
    15,001
    Location:
    Bothell, Washington
    They do make a low-inlet J bend

    [​IMG]

    A standard trap with a bowl that is too low for the trap arm.


    [​IMG]

    J Bend with low inlet
    http://www.keeneymfg.com/

    [​IMG]

    J bend with low inlet, installed.
    They make these for 1-1/4" and for 1-1/2"

    [​IMG]

    Putting a granite counter top on a 30" cabinet and undermountng a Kohler Caxton bowl pushed the drain a bit lower. The lo-inlet J-bend fixed that.
    Last edited: Apr 6, 2013
  8. Terry

    Terry Administrator Staff Member

    Messages:
    15,001
    Location:
    Bothell, Washington
    Here is a reversible p-trap that works!

    [​IMG]

    Dearborn makes a p-trap with a J Bend that can be reversed.

    Dearborn Brass P9703W
    Last edited: Apr 30, 2014
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