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Thread: S Trap / vanity sink drain / vent

  1. #1

    Default S Trap / vanity sink drain / vent

    Hi. Yet another newbie question...

    I am 90% done with a complete master bath renovation and was just going to hook the drain up the way it was which is with S traps. I've read to avoid the S Trap because of the possibility of siphoning and sewer gas entry.

    Is is critical to convert to P-traps going through the wall? What about installing an automatic vent device in the vanity itself?

    I read in a book that this is easy to do. The vanity is in place and it would be a bit of a hassle to remove (cutting out valves, etc.) See pic.

    Any suggestions?

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  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    Well, it appears you have another problem...unless the drawers are quite short, you won't be able to close them with the water supply line where it is. Is there a vent? Doesnt' look like it. An inspector would likely fail this install.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default trap

    You should have asked the question when you were 10% started, not 90%. Even then it might have been difficult to properly vent the sink.

  4. #4
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Yakima WA


    Most of the pro plumber really dislike the AAV, but in reality, unless/until they malfunction sometime, they will do the job. They must have easy access for replacement. You are going to have a drawer problem. You could shorten them so there would be space behind them. What you should have is the drain in the wall, but you'd still have some problems with the top drawer. I would have used a vanity that had doors in the center, then it wouldn't matter where the drain is located.

  5. #5


    The water supply lines are fine, as the drawers don't go all the way to the back. And yes, i should have researched the drain work earlier. I did have a licensed plumber do the rough-in plumbing for my shower. i should have asked him about the drains. I just figured that i would hook them back up the way they were...never thought a 20 year old house would have code issues

    shoulda woulda coulda... I may try the aav. If they work, fine. Otherwise, i'll bite the bullet, remove the vanity and call in a pro.




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