Hello,me and granpa are taking on an addition in our house we got everything else liked.We are doing the plumbing on second floor.Roughing in a new bath from scratch,I am just trying to help old man out,you know they know everything!!we screwed toilet flange down found a bay we are going to bring 3″ up.all the plumbing will be on one wall if it helps explain a little better.from left to right sink,toilete,bathtub.we have a straight shot to toilete hes thinking on throwing a 3 by 2 y before toilete and shooting for the tub with 2″ on the way to tub he wants to 2″y up for sink.then venting out of house.all within venting limitations 8’on 2″ pipe 5’on 1 1/2.So will 1 2″ vent pass inspection on a bath like that.or do we have to run a seperate line up for tub or sink Thanks for INPUT.