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Thread: S-Trap

  1. #1
    Join Date
    Mar 2007
    Iron Mountain, MI

    Default S-Trap

    This newer house (10 years or so) has an S-trap under the kitchen sink.

    The trap drains into a larger size tail pipe. Does this make this set-up acceptable?


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  2. #2
    Join Date
    Mar 2007
    Columbus GA

    Default Re: S-Trap

    You were right to call this out, it is not installed correctly.

    ' correct a wise man and you gain a friend... correct a fool and he'll bloody your nose'.

  3. #3
    Join Date
    Mar 2007
    Lake Barrington, IL

    Default Re: S-Trap

    Simple rule of thumb - No S-Traps.

    I once heard from a knowledgeable instructor that S-traps in older homes (70-80 yrs) can be allowed. But as far as I know, water and air vacuums behave much the same way today as they did years ago.

    Eric Barker, ACI
    Lake Barrington, IL

  4. #4
    Join Date
    Jul 2008
    Snowbird (this means I'm retired and migrate between locations), FL/MI

    Default Re: S-Trap

    Answering the actual question of the original post, nothing about this set up is right. I will outline some concerns, and possiblities below, BUT, this is unqualified work, and improper use of materials.

    It is not even a "proper" "s-trap" even if could be permitted. second half is a piece used upside down and the slip connector is upside down. The DW tailpiece is used correctly in location or orientation, and the DW drainage hose is not attached to anything (note water spillage out of DW tailpiece arm).

    There are more than one "model plumbing codes" in use, and several areas which have completely self-authored plumbing codes in the United States. Many areas which adopt a model code(s) do so with at least some modifications or ammendments.

    Old times some homes were fit with "house traps", thought to protect the residence from vapors/gas from the main sanitary/sewer - hence some areas allowing existing S traps for a "time" in "certain installations", etc. baring other modifications. Clog/scour issues with same. Double trapping issues as well, left "grandfathered" but removal when other areas worked on or additional loads installed to plumbing system, modifications (back flow checks, mod. stack vent location, etc.).

    On a recent thread, Ron Hasil made a comment regarding a pictured installation where a kitchen sink trap arm went to a stack 2, 3 or 4 trade sizes larger in which was capped off above. At a certain size and height ratio it was and may still be an exception in certain configurations thought to provide enough of a buffer to avoid total trap syphoning when large sudden inrush dranage avoiding a slug/suction to a horizontal running trap arm. It requires careful application, calculations, design of drainage and venting provisions, and is rarely, legally, employed (where permitted).

    That method could have been orginally intended here, but later NON-PLUMBER (apparent sink replacement by DIYer) has altered it.

    I see several issues here. First the dishwasher is installed. Not usually approved for segregated recycled gray water systems - presume this may have also been DIY post original construction/plumbing design/inspection.

    The sink tail piece with the DW inlet is TOO LOW in conjunction with the trap. This is a health hazard/cross contamination issue to both the DW and kitchen sink. The connection of the drainage from automatic dishwashing machine to the horizontal sink tail piece when properly installed and oriented well above any drainage direction other than a true vertical drop. This needs to be a measured distance above a trap weir depending on size. This requirement is in addition to an intermediate high loop, check valve, or integral loop for the DW drainage itself.

    Next the stack below has been shortened at full size to just above the cabinet platform and further reduced. This needs to be extended at full size to a height above a trap arm/fixture branch for the exception Ron Hasil discussed on another thread and we'd have to know proximity to the vent, etc. and what is going on below, etc.

    Joe Arcaro,

    Please go to your profile (you can use the "user cp" link on the left of the blue bar at the top of each page you view when logged in) and please enter something in the "Location" field, then click on the "save changes" box below it on the page. It is next to impossible to address any question you may have with specificity without knowing your location at least minimally, i.e. (state/province, country). Thank you in advance for your consideration.

    IIRC you roam the NE Wisc area and the Upper Penn. of MI??

    I would suspect the area is remote (recent cabin thread) and is on private waste system, either septic, cesspool, composting waste, and other grey water treatment, segregated drainage system, or tank which may be pumped??

    It might be the system was designed with a servicable trap and due to remote private "system" and plumbing system design, and such may have been designed and employed legally for non-year-round heated and occupied remote "camp", "cabin", etc. I would want to know first if that was the case, the characteristics of the system, and which state, county, or if in federally controlled lands (such as national park lands, etc.) the subject was located before I offered a definitive opinion one way or another as to the general question of "S" trap on kitchen sink.

    However, I believe that it was originally as the type situation discussed on another topic thread (reference Ron Hasil's comments earlier). Whether or not there were originally a multi-compartment sink or not, it seems the DW installation configuration and modifications above and below are DIY or unskilled handy-work, and that the stack even if originally a buffered and not vented one, one meant to accept a horizontal trap arm has also been modified. The "big box" piece kit used above for the two comparment sink is not a correct design item either.

    - but in the meantime the tail piece/dishwasher drainage installation/elevation in relation to the trap/drainage change in direction(s) needs correction - no matter what, and at present is a health hazard. It should be at one of the compartments above waste outlet below the basket and with an elevation before and well above a transition to or receiving drainage from horizontal. It should have additional vertical drop before any change in direction (including trap retention).

    in the interim, and in summary: No, nothing about the set-up is acceptable, no matter what the local code may be, the system present, or intent of the DIY unskilled work was; and yes a licensed plumber would be a great recommendation regarding inspection of the system, and to design remediation (AND DE-CONTAMINATION) recommendations and cost estimates. HTH.

    Last edited by H.G. Watson, Sr.; 08-07-2010 at 12:43 PM. Reason: Add request to original poster to add location information to his profile.


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