I have a double sink in a bathroom set up as in the picture below.
Another bathroom is behind the visible wall, and a new sink will go up against this wall (so the dual sinks will be back-to-back) with the new single sink.
The drain and vent-pipe is 2" and goes to a stack of 4".
Can I add this new single 1.5" drain to the existing wye and have all 3 sinks go down the same drain?
Would I add the new sink above the wye, or just below?
I believe code is that 3 lavatory sinks are allowed for the 2" drain.