Plumbing Stub-up questions

[elmach]

In my basement, in the stair wall there is a probably 4" PVC stub-up with a cap. When the cap is removed there is a metal ring with a fiberboard plug (see photo).

Anybody have any ideas on what this may be? Hoping it is a toilet drain stub, but not sure what is up with the plug and how to extend the toilet drain to the pipe.

Assuming I would need to cut the concrete out say 20-inches or so from the wall and install a toilet ring and connect into this pipe. Why would the stub be in the wall instead of set out the proper distance for a toilet install? Or perhaps it is not that at all - any ideas?

Thanks in advance.

 

[Matt30]

You're on a sewer I'm guessing?

That's not a toilet. Probably your clean out for your backwater valve.

I haven't ever saw a cover like that though, so I could be wrong

 

[Mr_David]

what are the other 2 lines on either side of it?

 

[elmach]

Yes, I am on a municipal sewer. Not positive what the other two ABS pipes are, but I would assume the one on the left to be the vent for the floor drain by the water heater, and the one on the right to be the drain for the clothes washer on the second floor above (all other drains being accounted for elsewhere. The small PVC on the right is the clothes washer overflow pan drain which spills onto the basement floor which then slopes to the floor drain.