: I have posted a picture of the very simplified layout for my bathroom drain plumbing. See it at:
: I'm in the planning stages, and at this point I have a pretty basic understanding of what needs to happen for this all to work and meet code. Once I have a better plan, I'll have it approved by the inspector. However, at this point I have some questions. In reference to my picture:
: 1. Does the vent system work properly as I have it shown?
: 2. Are back-to-back sinks using a double-tee permitted?
Most codes require a double fixture cross, using 2" on the bottom.
: 3. I don't show all of the bends which will be necessary to make this work, but is it okay to have two or three bends in the vent lines back to the main stack, and one or two in the main stack?
Using bends for the vents is okay.
: 4. Do I have to keep the main stack vent at the same size pipe (4") or can it be smaller?
You may check with your local codes, UPC expects theequivalent of 3" for the home, is 3" is exiting. A 2" vent will work for a bathroom. For this reason, you will see in most homes, two 2" vents and one 1-1/2" vents through the roof. If you have 4" going out from the home, you will need theequivalent area of a 4", and since you are only having one vent, then 4" would be fine.
: 5. I've shown an alternate attachment for the tub drain... Is there any reason to do that?
The tub drain can't come of the toilet are they way you have it drawn. I would put in a wye fitting below the tee for the toilet and run aseparate line to the tub, and vent it as you have pictured.
: 6. Is there a minimum/maximum slope for vent lines? No minimum for vent lines.
Waste lines drain at 2% or 1/4" per foot.
The "clean out" should be the same size as the line it cleansout.