I have an older bathroom that I am redoing and the sink drain went through the floor with an "S" trap, which I understand is not allowed with new construction. Is there a way to go through the floor and have a legal trap or should I go with a "P" trap and put the drain in the wall? I have already removed the plaster and the studs are exposed. The main question that I have is can I have the sink drain run approximately 2 1/2' feet and then go down and tie into the tub drain? The point where the line turns down will also go up as a vent. Please see the attached representation. The sink drain will be 1 1/2" and the tub drain will be 2". Is the vent considered a wet vent? The drawings that I have seen show the vent going up above the drain line. Can I share the drain line as a vent?

Thanks,
Tom

Yes, you have the tub wet vented by the lavatory roof vent. Good luck, Tom