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Thread: Plumbing pedestal sink under floor

  1. #1

    Default Plumbing pedestal sink under floor

    I am ready to install a pedestal sink in my dpwnstairs bathroom. It seems to be easier if I were to plumb the main drain down through the floor and then install the p-trap and additional piping to the main line (unlimited access). Is this legal or should I try to pipe the p-trap above the floor?
    Last edited by llt01; 03-20-2006 at 07:38 AM. Reason: additional information

  2. #2
    Plumber jimbo's Avatar
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    What you are proposing is an S-trap, which is disallowed by all plumbing codes I Know of.

  3. #3

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    Please correct me if i'm wrong. Doesn't a P-trap come down vertical from the drain then form a 180 deg loop up then elbow 90 deg to a horizontal run? This is what I would like to do, if I can. Is there a specific measurement the P-trap needs to be from the sink's drain?
    Last edited by llt01; 03-20-2006 at 08:11 AM.

  4. #4
    Plumber plumber1's Avatar
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    No it would then go through the floor and be re-plumbed to a different place.
    Yes it goes horizontal then.......

  5. #5

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    I don't think you should do what you're proposing. I understand from your original post that you want to install a standard p trap - you just want that trap to be below the floor, instead of a few inches under the sink.
    Codes dictate that the trap be located no greater than a certain distance (I think it's 24").

    I haven't found a technical reason for this, but I *believe* it has to do with the fact that water falling from a greater height might push the water out of the trap.

  6. #6

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    Please See Attached File
    Attached Images Attached Images  

  7. #7
    DIY Member casman's Avatar
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    I believe prashter is correct there is a max length to the vertical drop and I think its to prevent water due to its drop from being pulled out of the trap.

  8. #8
    Moderator & Master Plumber hj's Avatar
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    Default trap

    you cannot do it with the trap under the floor. Even if you could you would still need a vent. Installing the "P" trap above the floor, the way you describe would create an "S" trap out of the "P" trap. You could create a serious drainage, and odor, problem if the pipe from the drain to the trap were that long.

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