I have added a sink to my bathroom, since I am remodeling it, and need some help with the DWV system.

Below is a photograph. I have highlighted the existing 2" vent in red, the new 1-1/2" vent in blue and the new 1-1/2" drain in green.

I cut the new vent into the existing vent that is supporting a toilet, sink and shower/bath, in the adjoining bathroom, and the kitchen sink. Is adding a sink to this vent, with a 1-1/2" vent line, a bad idea? If I step it up to 2", would that make much of a difference? I have read that a 2" vent can support 8 fixtures, is this true?

Also, the drain is a little high. It starts at the stack at 19" on center and ends up at 23+" at the new sink location. The only place I can move the sanitary tee is to between the purple lines on the stack, would this be too low?

http://i275.photobucket.com/albums/jj316/piperca/SDC11165-1.jpg?t=1254713420

Has a permit been pulled and will it be inspected? I can se several problems right off the bat.
1) By discharging the lavatory into a vent stack that's servicing a bathroom group and a kitchen sink you have converted the vent stack intok a stack vent and wet vented all those fixtures.
2) We rough our lavatories ib at 18". You're coming in way too high at 23+ inches.
You may not be able to install a pop-up waste.
Your pipe sizing i fine for the lav alrhough I'd like to see a 2" drain line in place of the 1 1/;2" one and I'd like to see a clean out added on the raiser. I've got a hunch you're going to need one on that long run. Good luck, Tom

The drain was already plumbed into that 3" vent stack, all I did was extend it to the other side of the room and add a vent. I used the existing 2" vent as a location to vent the sink. Should I plumb in another sanitary tee into the stack and run a dedicated vent for the sink? Also, there is a cleanout located on the stack, below the drain. The total length of the drain is approximately 15 feet... the photograph is deceiving.