Not your usual S-trap question

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JenaK

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So, the hubs and I are working on an update for the little powder room on our 18 year old home here in GA. We've managed to pull out the builder-installed pedestal sink and are ready to install a new cabinet, sink, etc. Because the water lines and the drain all come up from the floor and not the wall, I'm going to have to do some "creative carving" on the new vanity cabinet. It would help matters a bit if we could install an S-trap from the sink drain tail piece over to the drainage pipe going down into the floor. Now, after doing some reading, I learned that s-traps are not to code and P-traps are--Then I wondered why the heck we had NO-trap--it was just a straight pipe going down to the floor. Then I went downstairs to our unfinished basement, looked up, and *voila* there it was. The p-trap is below the floor of the bathroom. (Hope we never drop something expensive in the sink drain . . . Doh!)

So . . . my question is, because we still have a p-trap, would it be okay to install the s-trap to bridge the distance between the current drain and the tail piece, or do I just need to suck it up and sacrifice the drawer in the new cabinet to keep the existing "straight down" configuration?? I'm attaching pictures below of the existing set up and of the p-trap I took when I went to the basement.
 

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Terry

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You can't install two traps on the same drain.
If you keep the underfloor drain, which really has too long of a standpipe to work right, you would just 90 over to the sink tail piece.
 

Jadnashua

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What can't be seen in the picture is whether that existing trap is vented. There's a limit on how long the standpipe before the trap can be, and this exceeds that limit.
 

Cacher_Chick

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I would remove what is there and install a riser back tight against the wall with a sanitary tee at 15-18" above the floor and then an AAV on top as high as it can go and still fit behind the basin. Then you can install a P-trap where it belongs.

The supply lines should be spaced 12" apart and the valves positioned so you use them easily.
 

Basement_Lurker

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With an exposed ceiling from below, most of the guesswork is done for you. There's no reason why you shouldn't tear into that bathroom wall and recess your dwv and supplies like they should be, and install proper backing for your pedestal while you are at it.
 
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Hey, wait a minute.

This is awkward, but...

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