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enter image description here

This is under a bathroom sink in the house we recently purchased. It was likely done to limit the vertical space taken up by the P trap.

Is it likely to cause a problem, and/or is it a code violation (US, Oregon)?

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  • It looks like they did it for more storage space underneath, yes? I don't think it's a problem, no different than a drop like that somewhere downstream of the trap. *However; I can't tell how tight those elbows are from the picture. If they used tight turn ells designed only for vents, it's not good (code violation). Commented Apr 23, 2016 at 2:33
  • Legally it's still an S trap, weather you want it to be one or not.
    – lowercaset
    Commented May 1, 2016 at 1:44

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I believe Oregon uses the UPC as the basis for their state/local code. Under the UPC S traps are illegal, and that's what you have there. S traps are illegal because they can cause the trap seal (the water that prevents the sewer gasses from entering your house) to siphon out.

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  • Every picture I can find of an S-trap shows the exit pipe going vertically down through the floor, which makes sense with respect to the trap seal siphoning out. In this case the exit is the standard horizontal pipe out the back. Commented Apr 27, 2016 at 1:55
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    @JimGarrison: The distinction between a P-trap and an S-trap is that in a P-trap the vent connection is higher than the bottom of the trap.
    – supercat
    Commented Sep 1, 2016 at 23:40

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