Forum Title: P trap variations
This has probably been discussed somewhere, but I could not find it... so here it goes (I apologize in advance for the elementary nature of the attached images): I have three new vanities and one new tub to install but have space constraints for the traps that need to go in. The drain from the wall is just above the bottom shelf of the vanity - effectively making it impossible to place a standard trap without cutting the vanity. So the question is this, can a p-trap be installed above the wall drain and have two 90 degree (or 45 degree) elbows route the water down into it from the trap? See the attached image figure A for a better visual Also, with respect to "p-traps", typically the drain goes straight down into the U part of the trap. Then the flow goes back up until it hits the 90 that sends the flow horizontal. Does it matter what angle that horizontal extension comes off the U portion of the trap? Can it go back over like a loop or is this a big "no-no" for some reason? I would love some explanation on this subject because one guy told me that it makes a difference whether the final bend in a P trap goes straight back vs left/right/over... I don't understand the physics of why that would make any difference, but maybe someone can shed some light on it for me. See figure B and C for a visual. I would like to use the "loop" option (figure C) for the tub trap. Does anyone see an issue with this? If anyone can refer me to some technical literature, that would be helpful too. Thanks in advance
Category: Plumber Post By: PENNY ACOSTA (Salem, MA), 01/23/2017

Figure A and B are against code, as the height difference between the outlet of the trap and the attachment to the vent is too great. This creates a situation known as an S-trap, and can cause the trap to siphon itself empty when the fixture drains. There is no issue with Figure C that I am aware of, other than that it looks kind of funky. I have had to do the same thing many times, and have encountered no problems with it.

- PHYLLIS RUSSELL (Bayonne, NJ), 09/24/2017

Ok, Figure A & B are no good. I understand how they could syphon dry from a physics stand point, but there would need to be a lot of negative pressure for that to happen and the actual stack/soil vent is less than 2 feet away from those fixtures. I've set both of those configurations up already because I did not want to destroy the furniture, nor did I want to open up the wall (which by the way would have required the exact same pipe bends but in the wall rather than out of the wall). Both have been extensively tested and no syphoning issues have been observed. However, for what it's worth, I would like to have everything up to code... so if there is a proper solution to match drain heights, I would love to know about it...any suggestions?

- STANLEY REYNOLDS (Baton Rouge, LA), 09/28/2017

Open the wall and move the santee to where you want it. You can raise it and move it left or right by turning the trap arm parallel to and in the wall with a 90 fitting coming out of wall where you want it. You can change the direction of the trap arm with not more thanone 90 degree or two 45 degree fittings.

- MARTIN MYERS (Richardson, TX), 10/07/2017

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