[amakarevic]

i am building a powder room on the 1st and a bathroom directly above (but naturally larger) on the 2nd floor. a 4" main stack goes conveniently in a corner of both, which is vent only until it reaches the 2nd floor toilet, then both from there down, including the powder room.

the space between joists under the powder room is tight and occupied with a lot of infrastructure already (electrical) as there is a basement apartment under. so i was gonna go with a 3" flange. was wondering if there is any advantage to going all 4", i.e. if the waste goes down faster in case of a wider pipe.

thanks