I'm ramping up for a full basement remodel and I'm wanting to be sure I'm fully covering my bases on the plumbing here-- I've heard too many horror stories. What I'm dealing with is a basement that's fully below grade, with plumbing already stubbed in for a shower drain and toilet. The main soil vent pipe for the entire house is 16" or so behind the toilet rough-in (which plumbing for both upstairs bathrooms are also tied directly into, venting through the roof), and only a few feet away from the shower drain.
1). Is there a way to determine if this shower drain already has a P-trap below the slab? I have to assume it does because there was a shower there before (just tore it out)...but I'd hate to rip out the concrete just to be sure-- any other tricks?
2). Because of its close proximity to the main soil vent stack, is this stack itself sufficient venting for the shower drain as-is? Or is cutting a hole in concrete my only option here? Again, it's only maybe 2ft from the stack, so cutting out concrete, routing a new vent after the P-trap (assuming it's there) and then ultimately tying that vent right back into the main stack seems like overkill. I feel like the drain should...drain no problem being that close to a 4" stack already.