Water flows downhill. Gravity and all that. Trace the sewer from the upstairs bathroom and/or kitchen to where it exits the house. Does it exit through the basement foundation wall (i.e. above floor level) as in the picture below? If so, a basement bathroom will need a sewage ejector pump to pump the drain water up to that level, even if the sewer exits the house only a foot above the basement floor. Picture applies whether or not you are on a septic system or a municipal system.

I forgot to mention that yes, the sewage line exits the house just below the first floor level, so the basement is all downhill. Whether or not I needed a sewage pump wasn't in question, my main questions were about the stubbed out PVC pipes and what my choices are for them.

I'll post pictures tonight or tomorrow. I looked again last night and the circle under the stairs has a pipe coming out of it, so it's likely a lid to a sump I think. And I doubt the builders went ahead and installed a sewage ejector pump in there.

One of the PVC stubs has a little black pan around it in the floor, and another one has a smaller pipe coming up next to it. There's also a PVC pipe coming up through the stud wall, and I'm thinking this is probably a vent line?

Like I said, I'll post pictures soon, but anyone that can help identify the pipes, or what is likely under the lid of the sump, please share. I'm very curious where all the PVC pipes under the concrete floor go.

Thanks!

Here are a couple of pics. If anyone could help me identify what the pipes are I would appreciate it.

And these too please.