Some one has asked before i'm sure. Question I have a single sink in a bathroom now and want to remodel and add a double sink for the kids. It has a two inch vent that takes care of the toilet and the sink. the 1-1/2 for the sink drain, tees into the 2" vent. I believe this is called wet venting. My question is will the 1-1/2 allow for the two sink vanity? and will i be under sized on the 2" vent by upgrading to three fixtures.