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Thread: Lav trap on larger trap arm: actual problem?

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  1. #1

    Default Lav trap on larger trap arm: actual problem?

    I have a 2" trap arm for a lav, and just realized a 1-1/4" lav drain can't
    use a 2" trap. The UPC shows the trap arm size must match the trap
    size, but does anyone know what problem a 1-1/4" trap on a 2" trap
    arm would cause? Self siphoning should actually be less than a smaller
    sized arm, so I'm not sure what the problem would be if I just go ahead
    and put the 1-1/4" trap on.

    Dave

  2. #2
    Master Plumber Redwood's Avatar
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    Default

    Is it the I.D. of the pipe that measures 2"?

  3. #3
    Moderator & Master Plumber hj's Avatar
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    Default trap

    Forget what you think the UPC says about arm and trap sizes. Install the trap. If you have the proper venting it will not siphon regardless of the arm size, and if you screwed up the venting, then it WILL siphon regardless of the size.

  4. #4

    Default Re: Trap

    So it sounds like all I have to worry about is inspector confusion
    on the final.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Default trap

    You are confused. The inspector will not be.

  6. #6

    Default Re: Trap

    Oh. So how am I confused?
    And what convinces you the inspector will not be?

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