I need some expert advice. I'd like to finish my basement and am trying to figure out the bathroom. I'm not the original owner, so I don't have the plans for the house and I'm trying to figure out what the heck the builder had in mind for the rough-in.

In the location that makes the most sense (the basement is in an "L" shape) to put the bathroom, this is the only thing that's there:

21344

I'm assuming this is a 4-inch drain for the toilet, but there's nothing for a sink (I'm not worried about putting in a shower). But this thing is only 6 inches from the exterior wall.

There's no vent pipe anywhere on this wall. There are other pipes coming down from the ground floor elsewhere in the basement, but there aren't any other obvious drains such as this one.

What in the world am I supposed to do with this?? (thank you in advance)

It's jack hammer time. Locate nthe house main and your rough in should go down like this.Toilet connects to the house sewer. Lavatory connects to toilet drain and runs a vent off the top the stubout tee out the roof or revents back into a dry vent in the attic.. The toilet wet vents through the lavatory vent and the shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes and also The Standard Plumbing Code Book in 90 percent of the country. Check your local codes to make sure you're not in the excluded 10 percent.. The vent off the lavatory may be run out the roof or revented back into a dry vent in the attic or if you're reventing back into a fixtures dry vent you must make your connection at least 6 inches over that fixtures flood rim. Good luck and thank you for rating my answer. Tom

As per your posted photo - what you have is a clean out, not a toilet drain set up. As Tom said, you will have to cut open the slab, locate drain, cut into it and install appropriate fittings for toilet and sink.

Thank you both... seems like it's a bigger job than I anticipated.