We have a bathroom rough in in a basement with three pipes up from the floor one is obviously the toile but how do we know which is vent and which is drain? Or are both drains and the rough in is already tied to the vent?:

We have a bathroom rough in in a basement with three pipes up from the floor one is obviously the toile but how do we know which is vent and which is drain? or are both drains and the rough in is already tied to the vent?:


The big pipe is the toilet. The 2" pipe in the wall will run up inside the wall to a 2"sanitary tee stubed out to pick up the lavatory and continue out the top of the tee as a vent for the group where it will go out the roof or revent back into a dryvent.
The 2" pipe out in the floor is a shower drain, however if it is setting in the center of a 14X14" square hole then it's a tub dapout for a bathtub.
Good luck, Tom