I'm remodeling my bathroom. I need to move my vent stack to make room for new bath design. The toilet is currently vented with 3" cast and the main soil pipe is 4" cast. The old sink was not vented. My plan is to vent double sinks with 1.5" pipe and the toilet with 2". I will then tie them together below roof and extend through with 3" pipe. Is it ok to vent a toilet with 2" pipe? I only have access to a 2x4 wall to run vent pipe through. Any help or suggestions would be appreciated.