Home made P-Trap

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by rmateyko, Jul 8, 2008.

  1. rmateyko

    rmateyko New Member

    Jul 24, 2007
    I have a problem - see related post "How many elbows". I need to raise a p-trap in a joist bay in a basement where I am building a bathroom so that i can drywall the ceiling. The p-trap comes off a bathtub in the bathroom directly above.

    If i raise the p-trap I need to cut a hole just above the existing p-trap hole which will mean i have two holes each 2 inches in diameter in a 7 inch deep joist in very close proximity - not good.

    Is it possible for me to construct my own p-trap using elbows and a piece of drain pipe. So instead of it being a "j" like shape it ends up being a "u" type shape. That way I can stick the horizontal part through the existing joist hole and connect to the bathtub on one side and the rest of the drain system on the other side.

    the problem I am having with standard type plastic p-traps you buy at home depot is that the trap weir ( if that is what you call it) creates a fixed offset. to move the bottom of the p-trap up i have to cut the hole higher.

    I have included some drawings

    thanks ahead of time


    Attached Files:

  2. leejosepho

    leejosepho DIY scratch-pad engineer

    Nov 23, 2006
    disabled-retired industrial fabricator
    200 miles south of Little Rock
    I *think* I remember "back in the day" when there was no such thing as a ready-packaged trap and *everybody* had to construct their own. A "j" is really nothing but a "u" with one side extended, so yes, I believe what you are considering should work just fine as long as all of the "u" is actually there.
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    You can't (or shouldn't anyways) make the drain path go up from the output of the p-trap's normal outlet...from the outlet of the p-trap, it should always go down so gravity can do its thing. Failure to follow that rule will lead to slow drains and clogs of hair, etc.
  5. jastori

    jastori Member

    May 2, 2008
    From the side (horizontal) view, you want to duplicate the rise and fall of the "store bought" p-trap. That is, there should only be one "trap", and the drain should have a downhill slope immediately after the trap, all the way to the stack. The total depth of the trap does not need to be exactly the same as the store bought, but you would want it as close as possible.

    From the top view, extra bends in the path of the trap and drain should not effect the function of the trap, so long as they are gentle sweeps, and as few as possible.

    Hope that helps...
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