Connecting 2 bathroom basin wastes

[buildawall]

2 basins back to back, 2 separate bathrooms. studwall between rooms
Stack is about 2.5metres away. which would be best and meet building regs?

option 1: run 2 separate 40mm pipes to stack.
option 2: connect into horizontal soil pipe (Top of soil pipe with a boss) from each sink, about 1m away.
option 3: connect 32mm to 32mm then to 40mm, both sink traps anti syphon then to horizontal soil pipe or to the stack.

cheers

 

[motorbiking]

As long as you have a little drop, there is no reason not to have sink 1 short drop, elbow and run in to sink 2 T connector from a short drop in to soil stack connecting boss. As long as you comply with the splash back regs for any toilet connector. i.e. not opposite. I'd go up to 40mm as early as you can in the run.

 

[Madrab]

Best would be 2 separate (32mm) runs if it can be done, avoids any syphoning/gurgling issues. If not then use at least 1 antivac trap and increase 32mm to 40mm at the connection.