I apologize in advance. I know we DIYer's can drive you guys nuts sometimes. But, here I am.... - Building a basement apartment. My diagram is the basics of the drain plumbing in the floor. The 4" drain to the left hooks into the main sewer line of the house about 6' left of this new toilet. Everything else depicted is 2" PVC. The two yellow spots are 2" vents. They tie together and then make their way to tie into the vent system. When I planned this (last year) it seemed to me that it is essentially a legal wet-vent set up (?) and that the two 2" vents were/are superfluous. Is that correct? Now though, I'm wanting to add a laundry drain off the end there by the sink. Can I do that without adding a vent? If it has to be vented separately, how big does it need to be and should I tie it into the sink as well or just leave that the way it is? Thanks very much for any answers/advice you can provide.