hi rbly. I may be able to shed some light. First, i'll comment by adding what you probably already know.Originally Posted by rblystone
1. your jpg's haven't shown any venting at all; this full bath needs vents somewhere.
2. "main line is right underneath" I saw the pipe right under your shower space, in the center. That is not good if you intend your shower to have a center drain right above the pipe, because you need room for the p-trap, the little stub coming out sideways, and the fitting on the main drain!!
3. All traps are always P traps, AFAIK. The bottom of the p trap is down below the height of the main drain, otherwise is acts as an S trap, which is not good. Do not use drum traps either.
4. i think the right way to connect your shower to the main drain line is with a Wye and not a Tee, and if that is the case then the right way to refer to it, is to avoid using the term "Tee into".
Depending on how you arrange your vents, the shower may be vented sufficiently, so it is not possible to comment on whether or not your shower needs venting "per se" all by itself. Although some could say that you need three vents for three drains...
General rule: Plan vents first. Then shoot drain (after its trap) over to the vent, so it is now vented, and then turn drain to the main drain and connect with a Wye. Everything depends on where you vent upstream of the shower p trap. AFAIK.