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!


Here is the current config.


2 Answers 2


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.


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, 2016 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, 2016 at 1:38

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