Threaded vs Glued PVC floor drain pipe in cabinet bottom

**Hillel** · 12-02-2012, 01:36 PM

Hello Everyone,

I am installing a corner sink vanity that I built from an old mahogany tabletop in my dining room. The plumber set up the supply lines in the wall, but the only place for the drain was to come out of the floor. The drain pipe is 1.5" PVC. The only way to swing the vanity into position around the pipes is to cut the drain pipe below the cabinet bottom height, glue a coupler into place, and then install the vanity and insert the rest of the PVC pipe through a hole in the cabinet bottom. The coupler ends up hidden in the space behind the toe kick of the cabinet.

If the PVC pipe coming up through the cabinet bottom is glued into the coupler, then the pipe would have to be cut if the vanity would ever need to be moved. I would rather not have to do that. Instead of a coupler, I could use a threaded connection on the pipe inside the toe kick and cabinet bottom area. That way, the extension into the cabinet can be removed to move the cabinet if necessary.

Is having a threaded connection inside the cabinet bottom a problem for a PVC drain pipe? Is this asking for trouble where we might not notice a leak? Could there reasonably be a code problem with having a threaded connection beneath a cabinet bottom?

Thanks.
---Hillel

**johnjh2o1** · 12-02-2012, 02:47 PM

If the drain is coming up through the floor then you will have a S trap which is not legal. To make it correct you will have to use a AAV

John

**cacher_chick** · 12-02-2012, 05:19 PM

If you were using tubular drain piping into a trap adapter that would work. As John stated above, you cannot install a trap without a vent, as the trap will siphon and the sewer gas will come back up through the drain.

**Hillel** · 12-02-2012, 06:00 PM

Venting is not going to be a problem. This qualifies as an island fixture with an AAV and will be the only such fixture in the house.

The question is, is it safe to put a threaded connection for the PVC drain pipe between the cabinet bottom and floor, or just glue a coupler and deal with cutting the pipe later if the cabinet is moved?

Thanks.
---Hillel

**SacCity** · 12-02-2012, 06:19 PM

No problem with a threaded fitting.
Often I would use a flexible repair coupling for this type of thing.
Whatever works and is water tight is fine

**bluebinky** · 12-03-2012, 10:20 AM

Female threaded plastic pipe fittings need to be accessible (for replacement in case they split). At least that's how I read it (UPC)... hj, Terry...?

In my limited experience, I've only seen that happen with metal to plastic, not plastic to plastic though.

**Hillel** · 12-03-2012, 06:17 PM

Originally Posted by bluebinky

Female threaded plastic pipe fittings need to be accessible (for replacement in case they split). At least that's how I read it (UPC)... hj, Terry...?

In theory, this would be accessible for repairs. Remove riser with male threaded fitting, move vanity away from wall, and the pipe in the floor with the female fitting is exposed.

What is the chance of there being a leak with a threaded fitting that would go unnoticed while a glued coupler would not leak?

Thanks.
---Hillel

**cacher_chick** · 12-03-2012, 06:50 PM

A PVC threaded fitting will always be more likely to leak than a properly cemented PVC joint. The determining factor for me would be how much of a problem would it be to replace or repair in the future.