Hi guys,

I'm working on remodeling my bathrooms- they share a common wall, and I need to shift some the drains. Both bathrooms share a common wall, and I believe there is a 4" main line running out to the curb.

Can I plumb the system up according to the following?:

Details: (#1 refers to bathroom 1, #2 refers to bathroom 2)
1. Everything is within 3 ft of main line except for Sink #1, which is 5ft away.
2. Currently there is one 2" vent for 2 toilets/2 bathtubs/1 sink (#2). Aforementioned sink #1 has its own 2" vent.
3. Both 2" vents exit through roof.
4. currently everything is beneath concrete (soon to be removed) so I am not 100% sure of how piping below is done currently.
5. Single story, all plumbing would be beneath concrete.
6. all sinks/bathtubs will have their own P-traps.
7. Toilets appear to be 3"

Proposed:
(from end of stack -> curb)

Cleanout -> Sink #2 (and 2" vent) -> Bathtub #1 ( and 2" vent) -> Bathtub #2 (and 2" vent) ->Toilet #1 -> Toilet #2 -> 2" Sink #1 (and 2" vent) -> ->curb

Questions:

1. Sink #2 and Bathtub #1 are very close; they may be able to share same drain into main line. If so, can I use one 2" vent for both? (See 3 vent proposal 2)
2. If I use a Wye cleanout + vent, do I still need vents for question #1? (See 3 vent proposal 1)
3. If I rejoin 4 vents into 2 in the attic, do I need to increase the vent after 3" up through the roof?

Thanks in advance- I've already scoured the board for all relevant info prior to asking!

If wet venting's allowed in your area I would go with the second drawing. The only change I would make would be to lose the tub vent as it will be wet vented by the lavatory that wet vents the other tub.
Good luck, Tom