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My question is where to install a P trap on this configuration (Disposal is directly over the drain pipe). We are on conventional foundation, so is installing P trap under the house an option? We went from a double sink to a single deeper sink and there was only 6 inches of clearance so I took a chance with no P trap....bad idea. Sewer gas now coming in regularly. Any help with details and illustrations from a plumber would be much appreciated. Thanks!

Max

Here is the current config.

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You're going to have to put a trap in there somewhere. If there's enough space in the cabinet, you could do something similar to this...

enter image description here
NOTE:: All horizontal pipe sloped at 1/4" per foot.*

If not, and you have access to the plumbing below. You could reroute the plumbing, so the it comes up the back wall instead.

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While it might not be allowed by code for new plumbing, you can use an S Trap. You will have to rebuild things to get things aligned correctly, but an S trap is exactly what you need if you are trying to get this going quickly and in a pinch. Just make sure the drain is vented after the trap in the crawlspace so the draining water does not siphon the water out of the trap.

  • AFAIK s-traps aren't allowed (code) because they have the potential to siphon the water out of the trap - leaving you in the same position you were in with no trap at all. – brhans Jun 8 '16 at 14:00
  • An S trap is many times better than what they have now; and what is actually allowed is up to the code official. Sometimes they allow them. Granted if there is room to get a p trap into place, they would force a P trap. Also, not all s traps siphon the the water, typically its s-traps with no vent. I modified my answer to reflect this. – Damon Jun 10 '16 at 1:38

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