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Thread: S trap problem

  1. #1
    DIY Junior Member RobbyDIY'er's Avatar
    Join Date
    Dec 2012

    Default S trap problem

    Hi guys,
    I'm new to this forum and am looking for some suggestions regarding a s-trap underneath a newly installed sink. The problem I am having is that the sink drain makes a loud gurgling sound after water has exited down the drain pipe. If the s-trap is removed, the gurgling sound does not happen when water is draining. I have a suspicion that the sound may have something to do with the drain pipe from the sink leading to the main soil stack being too long and too vertical. It measures about 14ft long and it seems to drain just fine. What are my alternatives to a s-trap? Any thoughts on the cause of the gurgling sound? Thanks in advance for any input...

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
    Join Date
    Jan 2008
    Land of Cheese


    S-traps are not allowed by any plumbing code because their design causes the trap to siphon. This is what the gurgling noise is.

    Modern plumbing requires a P-trap at every fixture, and that trap must have a vent. The vent is what prevents traps from siphoning. The vent must rise from the trap arm vertically through the roof, or can connect to other fixture vents before it goes through the roof.

    Where I live, the plumbing code permits the vent for a 2" horizontal drain to be up to 8 feet from the trap, or 6 feet on a 1-1/2" drain.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    The best, most reliable method of venting is to vent to the atmosphere through the roof. But, if there's at least one atmospheric vent in your system, and the local codes allow, AND there's no reasonable way to run an atmospheric vent, they may allow you to use a AAV. This would allow you to use a proper p-trap configuration and the AAV would act like a vent. THey do wear out and need to be replaced, and they can't be used everywhere, but it may be the easiest solution to your problem.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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