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

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    DIY Junior Member zbdd2's Avatar
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    Default CAn the J bend in a p-trap be installed "backwards"??? J-Bend Lo Inlet

    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?

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    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.



    Last edited by Terry; 04-06-2013 at 11:52 AM.

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    DIY Junior Member zbdd2's Avatar
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    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 by zbdd2; 07-09-2009 at 12:21 PM.

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    Moderator & Master Plumber hj's Avatar
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    Default 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.

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    Master Plumber Redwood's Avatar
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    Even Watts made this mistake on their website product pictures...
    Oops! Click Here
    And might as well do it twice



    Problem is like HJ said they fall apart easy and leak...
    Last edited by Redwood; 07-09-2009 at 07:08 PM.

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    Forum Admin, Expert Plumber Terry's Avatar
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    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.

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    Forum Admin, Expert Plumber Terry's Avatar
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    They do make a low-inlet J bend



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




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



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



    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 by Terry; 04-06-2013 at 11:57 AM.

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