Re-submitted under new user id. Sorry.
If the trap stops the fumes why do you need to vent drains? Will they run slow? Why? It's not like a vacumn is forming in the line. I know it's the code but why?
I want to conect two toilets in the women's bathroom, one vent pipe will go through the roof , how do I conect them together so they will vent through one pipe, or is that the way to do it, they are in the same bathroom.

There are many ways to connect and vent side by side toilets in a public bathroom. Could you make a drawing showing me the layout of the entire bathroom, including all the fixtures and the main that you wish to connect them to. Will this be a back to back installation with the mens bathroom on the other sidee? Regards, Tom