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Thread: S-Trap Workaround

  1. #1
    DIY Junior Member zinc65man's Avatar
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    Default S-Trap Workaround

    Hi Everyone,
    Looking for a little advice. I have a vanity that has a "drawer" under the sink (see attached pic) so I'm unable to install a proper P-trap. That leaves me with the dreaded S-trap. But after searching this and other forums, I haven't been able to find an adequate answer to my issue. It looks like most S-trap issues are unvented, or otherwise attach to vertical drains. In my case, I have a vent only 4 inches away from the end of the "S". I just don't see a siphon happening. At the same time, I could envision possible gurgling. So here's the question, is this a rare instance where a S-trap is acceptable?

    As I see it, I have 4 options.

    a) Install the S-pipe as shown in the diagram.

    b) Raise the T joint about 5 inches and install a proper P-trap

    c) Cut the vanity and install a proper P-trap.

    d) Increase the horizontal distance between the trap and the other half of the "S" thereby converting it to a legitimate P-Trap. I've heard that I need at least 2 times the pipe width. If I have 1.5 inch ABS, would that mean a horizontal run of 3 inches? I think this would fit.


    My instinct tells me that the best ways to deal with this (in order) are b, c, and d. I'm hoping that no one finds an issue with a) but it's probably unlikely.

    Really appreciate any commentary.
    Thanks,
    Mike
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  2. #2
    Master Plumber nhmaster's Avatar
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    Raise the tee.

  3. #3
    DIY Junior Member zinc65man's Avatar
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    Default

    Well, by that short answer, I'm assume that a) the S-Trap is out. I figured as much. Let's further assume that to move the tee I'm dealing with cast iron and replacing tile that just can't be found or replaced. So I'd rather not do b) either.

    If I implement the d) solution, it'll probably pass code, but will there be gurlging? (In which case, this is not a viable solution for me). Is there any plumber out there that can tell me that "yes, that is legal (barely) and that should work correctly"?

  4. #4
    DIY Junior Member zinc65man's Avatar
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    Also, a quick image of what I mean by the d) solution. A P trap where the "run" is equal to twice the width of the pipe width. So, 3 inch run for 1.5 inch ABS. It's not clear whether this should be twice the width of the pipe or twice the width of the entire trap diameter (around 8 or 9 inches) using 1.5 inch ABS.
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  5. #5
    Illinois Licensed Plumber SewerRatz's Avatar
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    Thats still an S-Trap

  6. #6
    Master Plumber nhmaster's Avatar
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    solution D will never pass code either. No matter what you do you need a P trap configuration there.

  7. #7
    Plumber jimbo's Avatar
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    As long as you have a drop before the vent, you have siphon potential, and it will be ruled an S trap

  8. #8
    DIY Junior Member zinc65man's Avatar
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    Hi everyone,
    This morning I knocked out the drawer in the base of the vanity (which surprisingly also gives me more room to store stuff) and installed a correct P-trap. Thanks to those for addressing my specific vented S-trap question.

    I guess I knew what I was supposed to do all along. I read in one of my books (Do it Yourself, Casell, Parham And Eakes, 2007) that there was no problem with an S-Trap. Also, I read here

    http://www.homerepairforum.com/forum...traps-o-k.html

    about the "conversion" (with picture). The reason I decided to install a standard P-Trap was that about 90% of articles I read said to just avoid S-Traps, and 10% said that there was no problem. I'm one of those guys that always wants to know why? So in this case, why are these 10% of plumbers saying that it is ok? They seem to have "decades of experience" as well.

    Please remember that I've already installed a P-trap, so I'm on your side.
    I'm just curious as to an ambiguity in the code about run or something like that.

    Mike

  9. #9
    Master Plumber nhmaster's Avatar
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    10% are just plain wrong or uneducated I suppose.

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Default wrong

    That is because those 10% are either not plumbers or they are construction plumbers who NEVER have to work with traps. All they have to do is install pipes the way the blueprints show them and they will never create a need for "S" traps.

  11. #11
    Plumber krow's Avatar
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    Quote Originally Posted by zinc65man View Post
    Hi everyone,
    So in this case, why are these 10% of plumbers saying that it is ok? They seem to have "decades of experience" as well.
    10% of plumbers are lazy.
    10% of plumbers don't know the codes
    10% of plumbers are in their 90's (when they worked in the trade in 1950's, S-traps were allowed)

  12. #12
    DIY Junior Member zinc65man's Avatar
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    I think I get the message , thanks for all the help and opinions.

  13. #13
    Moderator & Master Plumber hj's Avatar
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    Default Not really

    10% of plumbers are in their 90's (when they worked in the trade in 1950's, S-traps were allowed)

    1. I am not 90, yet.
    2. I worked in the trades in the 50's.
    3. "S" traps were NOT allowed then and had not been for many decades. Even "crown vents" which were an upgrade to true "S" traps had been outlawed by the 50's.
    4. Your historical knowledge needs upgrading.
    5. I went to the site that posted that "revising an S trap into a P trap" diagram and explained that anyone who did that must have been fired from Home Depot, and received a somewhat nasty reply that ALL their experts are professionals and I should butt out.

  14. #14
    Illinois Licensed Plumber SewerRatz's Avatar
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    HJ, that site, ... wow. We could have some fun there. I think it was redwood that posted a link to an old 1910 code book that showed S-traps and my 1917 Ohio plumbing code book only prohibits mechanical traps and traps that have partitions. Also it goes into the allowed material a trap can be made of. I do love the old code books.

  15. #15
    Plumber jimbo's Avatar
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    That particular forum is "controlled" principally by two people, both the plumbing and electrical areas, and they get a little touchy when anyone tries to horn in.

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