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I live in a large Travel Trailer and would like to have more space beneath the sink for storage.

I'm buying a top mount rectangular vessel sink with hand pressed pop up drain plug no mechanism from taps to drain.

My question. Can I run a 90 or 60 degree elbow to short straight pipe from the sinks tail pipe to the trap?, A second 90 again to trap so it can fit tight to back wall, then slight angle down of connecting pipe going into the main drain/vent stack?

Does the trap need to be attached directly to and below tail pipe or as I propose, can it be bridged 8 to 10 inches away then surface mounted on wall... providing its installed at same height under sink it would normally be?

proposed rv plumbing

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  • This would be no different really from what you see under a double-bowl sink--the trap doesn't directly align with the tailpiece. That, and as you're in a trailer codes probably don't apply. Try it and see! P.S. "flush" doesn't mean "tight to". :)
    – isherwood
    Aug 5, 2021 at 19:10
  • Thank you. Ive been overthinking this. You are right, your example clears it all up.Flush... well as close as Ii can get but 1 inch off with insolating foam between because as you alude to, its an outside wall with at best 2" of insulation, under an enclosed area that doesnt exchange much heat with the open heated areas of my trailer. So I decided to make the undersink door a mesh design to aide in air re circulation and add 1 inch foam board on back wall and on floor of vanity, nicely hidden by 1/4 inch ply glued to it. It may be a trailer but I like an eye pleasing layout.
    – namwen
    Aug 6, 2021 at 18:12
  • Please take the tour so you know how to follow up with your post.
    – isherwood
    Aug 9, 2021 at 19:38

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My question. Can I run a 90 or 60 degree elbow to short straight pipe from the sinks tail pipe to the trap?, A second 90 again to trap so it can fit tight to back wall, then slight angle down of connecting pipe going into the main drain/vent stack?

As long as the trap arm (pipe between p-trap and vent pipe) length is at least 2x the pipe diameter, it's probably fine. But there is a slightly easier way:

Instead of using a straight tailpiece and an elbow, try a "garbage disposal tailpiece", which already has the elbow built in: enter image description here

This way the tailpiece will be higher than the trap arm: enter image description here

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    Some places call these an 'offset tailpiece' and they are typically used to provide wheelchair access at accessible sinks.
    – pdd
    Oct 14, 2021 at 20:54

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