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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)?

  • 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). – Jimmy Fix-it Apr 23 '16 at 2:33
  • Legally it's still an S trap, weather you want it to be one or not. – lowercaset May 1 '16 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.

  • 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. – Jim Garrison Apr 27 '16 at 1:55
  • @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 Sep 1 '16 at 23:40

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