Re: Common vented toilet and tub/shower using sanitary tee?
Posted by Deb on January 10, 2004 at 11:33:45:
In response to Re: Common vented toilet and tub/shower using sanitary tee?
: I have bathrooms back-to-back with a nice large stack wall in between. I want to rebuild one of the bathrooms, swapping the toilet and the tub (so that the toilet in one bath will be back-to-back with the tub in the other, and vice versa).

: I am going to add a second 4" stack teed into the main 4" vent in the attic, and wyed into the main 4" drain in the basement, so there will be a 4" vent behind each toilet/tub combo.

: Can I have the fixture drain from a toilet, and the fixture drain from a tub/shower, connect back-to-back into a 4" stack as a "common vent" using a double sanitary tee (using a 4"-to-2" bushing in the side for the tub/shower)? All the examples I've seen of common venting involve identical fixtures, not a tub and a toilet. And I've seen comments to the effect that back-to-back toilets should use a double wye instead of a double sanitary tee, but obviously a wye won't work for the shower since the split in the wye would be below the trap weir.

: Comments?

There is no reason to run another 4" stack. A 3" is adequate, the fittings cost less, and most importantly, take up less space. Side inlet sanitary tees are common. You are correct in your assumption (and the reasoning behind it) that you cannot use a wye.
The Pipewench

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