I thought my DVW plan was all set until I read Terry's response to someone about not having toilet waste washing past a wet vented shower. Hmmm. I'd rather do things right so the system works well without bubbling or siphoning.
The horizontal run in the space between my 2 upstairs baths is as follows (going downhill)
1. guest bath WC
2. new shower drain (runs about 3' to wye)
3. 3" vent stack to attic and out
4. Lav drain (has its own vent which shoulders into main vent)
5. master bath toilet
6. down turn into waste stack to basement.
All this takes place in a 6 foot run, so nothing is far from anything. Do I need to add a separate dry vent for the shower drain? Fitting one would be painful but possible using the space under the shower bench to add the upward fitting. From the wall, tying into an existing dry vent going to the main stack would be simple. That said, I don't want to go doing anything unnecessary.