Trap arm slope

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by tomcat22, Jun 25, 2008.

  1. tomcat22

    tomcat22 New Member

    Nov 28, 2007
    I just read in the pipe dope thread that the lav trap arm should have a slight slope towards the trap. How critical is that? I just installed my double sink drains and I had the trap arms slope away from the trap.

    Note that in a different double vanity installed by the builder 18 years ago, the trap arms slope very dramatically away from the trap and we haven't experienced any problems. Thanks.
  2. jimbo

    jimbo Plumber

    Aug 31, 2004
    San Diego, CA
    I don't know why it would slope towards the trap.....that would cause problems.
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  4. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    Traps arms should be sloping at a 2% grade "down hill".
    That is the same as 1/4" per foot.
  5. Gary Swart

    Gary Swart In the Trades

    Sep 1, 2004
    Yakima WA
    Ideally, give it a bit of a slope downward toward the drain. On very short lengths, even level will work OK, but never try to make water run uphill under gravity.
  6. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    IF there were a reason to slope UP from the trap it would be for any piping between the trap and the sink. AFTER the trap the piping slopes downhill.
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