As I dug into everything, I found that there may have been a toilet installed at one time where I am hoping to put a new one at, the only issue is there was concrete poured down the hole so it was not usable, so all new fitting were going to have to be installed.
My biggest concern is making sure I can pass code with how everything will be installed. I am hopeful that the existing vent for the old toilet will be sufficient for venting and pass code. I am okay if I need to add separate vents for the toilet and the shower, but would love it if I could just use what is existing.
The existing 1-1/2" vent seems to attach to the 3" main stack in the top floor wall somewhere above all fixtures, and the 3" main stack is vented through the roof. absolutely no water comes through that vent (not a wet vent)
Also, as far as installing the new toilet, should I use a 3" sanitary tee with a cleanout or would a 3" 90 long radius elbow be okay? not sure how often that clean out will be accessed if I am pour concrete back over everything.
See the attached pictures - I tried to get shots of what is currently installed (I will be replicating this design for the new install, but will be adding flange for toilet and drain for a new shower.
Looks like i can only post one picture at a time. I'll do another post with existing plumbing