Thank you all so much for your input. It was a frustrating process, learning not only more of the general code, but trying to figure out what Pittsburgh wants on top of that, but I can say that I've learned a good bit in the process, so that's always good. I've been looking at some posts on here about converting single to double lavs, and it seems to always be done with 2 traps and vents, though granted its often only 1.25" traps, which would reduce flow a bit. But, point being, it seems like double lavs are almost always plumbed with separate traps and vents, even if it would be feasible to trap them together. Why is that? Seems like the reasoning for this would carry over to a kitchen sink, which with everyone having disposals and dishwashers, gets a lot of abuse drain-wise. I think I'm actually sold on 2 traps and vents being worth it - it really isn't that much extra work or cost, and its only for one fixture. Even if I wasn't required to do so, I think I might do it this way. Agreed though that there is some point where you have to stop. I'm a fan of 2" vent and drain lines (rather than 1.5") in almost every case as well, so I guess I tend towards the overdo it to be safe end. I generally will only carry one lav on a 1.5" vent and 2 of anything on a 2", though this is conservative. My house ended up a bit like swiss cheese - lots of separate vent lines go up above the highest drain line on the 3" stack and tie in there - I also wouldn't accept a 2nd vent line protruding through the roof. My 3rd floor stack is almost more tees and wyes than straight pipe, haha. Go ahead and call me fussy, its true. Guess that's also why I have a home-run Pex water system with at least 2 shutoffs between every fixture and the manifold. And insulate all water pipes all the way through the house. Overkill, yes. But I'll never disrupt anything else in my house to work on something, and the hot water gets to my fixtures a lot faster, and the cold water gets there colder since it didn't absorb heat out of the walls, hot pipes, or drain lines. I also like that there are very few fittings that aren't exposed... less places to leak that are hard to get to. I'm not afraid to spend more time and money to get what I think is the best product, but I can definitely see how many people would not accept the cost of the way I do things. I do all the work myself pretty much, so extra time and material cost isn't that significant compared to the peace of mind I have living in a house that is done this way. To each his own... Anyway, thanks everyone who helped me work through this. I'll be doing it how I sketched in the one post. I can't see how it could hurt, other than a few extra dollars in parts and maybe a little less room under the sink.