You mean like this?
You can use 3" on your waste stack.
And yes, the upper floor needs to connect below the bottom floor or you will suck all the traps dry on the way down.
I am plumbing a house with 2 bathrooms located one over the other. The toilets will be positioned such that they will drain into the same 4" vertical stack. I was planning on connecting the 2nd floor lav & shower into the stack at the second floor level but I read something that said that you cannot drain a fixture above a WC and these would connect ABOVE the 1st floor WC.
My question is:
Do I have to run the 2nd floor fixtures down to the 1st floor and connect downline from the 1st floor WC or can they connect below the 2nd floor WC and be OK?
Thanks in advance for your help!
Wow Terry, that diagram looks crazy busy! LOL
This is what I was originally thinking...
You were thinking "wrong". You are thinking like someone who was told, "Anyone can do plumbing. All you need are some pipe, a bunch of fittings, and some glue".
Licensed residential and commercial plumber
Once a pipe becomes a drain, it can no longer be a vent with a few minor exceptions and this isn't one of them.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013
Mine had all of the proper drains and vents.Wow Terry, that diagram looks crazy busy! LOL
If you would like to see a wet vented version, it looks like this.
You could easily add a wye off of your main line with a vent between the toilet and main line, run the vent for the downstairs toilet up to the second story and tie in at 42" there.