Double lavatory drain offset

[Gregg G]

New construction, concrete walls with foam insulation.

Almost have the DWV rough-in complete, working to finish MB lavatories and shower. Tried to
do floorplan so that there were no water lines or drains in the outside walls. In the master bath
the two lavatories are against an outside wall though. It would be easy enough to route the drains
and water lines in the two "side walls", but this would use up a lot of space under the vanity and
require two vent lines - one for each lav/p-trap.

Terry explained a lot about the reasons for using two p-traps (one for each lav) instead of trying
to tie them together (one thing is to minimize length of pipe before trap to minimize potential for
smells). I also have seen sketches and pictures that Terry and others have shared that show the
correct way to do two lavs.

I think what I want to do is keep the layout just about how Terry recommends - use a "double fixture
sanitary tee" (not a plain double san tee, so that one drain won't flow try and flow across the tee instead
of down). I'll also run the trap arms along the "outside wall" (just have to router or hot-knife out a bit
of the foam insulation) and then run those into the "double fixture san tee". A 1-1/2" line will go up
along the outside wall for venting, and a 2" drain line will connect to the bottom of the san tee.
It turns out that there is a joist that runs very close to the outside wall, so it would be difficult to
run the 2" drain line straight down.

What will work is if I put in a 45 long elbow just below the san tee and run the drain towards the
front of the vanity for about 8", then I can put in another 45 long elbow to get the drain line pointing
down again. Any problems with this plan that you can see?

Kind regards,
Gregg G.

 

[Terry]

You can use 45's or 90's at the lower end.
It's a double fixture fitting.

 

[Sponsor]

 

[Gregg G]

Ha, ha! That's exactly what I need to do. I didn't think of it, but the way you have the drain pipe
routed at the bottom is so that it fits inside the "toe kick" of the vanity, huh? I'll do it like that and
then won't use any additional space inside the cabinet at all.

Thanks for the picture (worth a thousand words)!

 

[hj]

I usually install a cleanout below the DFF and use a 45 to go into the floor.

 

[RHinNorCal]

Any good ideas for back to back bathrooms, both with double lavs? Crawl space below... Terry's photo is so crystal clear that I want to use it - with the HJ mod. That being said, if I built the wall in between the two bathrooms out of 2x8, or doubled 2x4, would there be enough room? And can they share a single vent line?

 

[RHinNorCal]

Here's a pic of the back-to-back double sink challenge.