This is not a home I inspected, but any idea why this condition might exist? I’m thinking this is a homeowner bathroom remodel solution to installing a drain for a sink where there used to be a tub.
Looks more like an overflow or PRV drain line into the 2 1/2" tub main. A copper line has been tapped into a 1/2" galvanized supply line as well. Is there a new laundry area above with a water heater. That’s my guess.
What’s PRV? If it’s an overflow wouldn’t there be a drain pipe near it?
Kenton the answer lies above (nopunintended)
It looks like a 3/4" drain line that’s be directed into the old Ptrap of a former tub. I wouldn’t think a sink line however, too small.