I'm doing roofing, and looking at a roof vent pipe (e.g. a plumbing drain waste plumbing penetration). It is 1.5" galvanized pipe original to the construction. I see it emerge from the top plates and up to the roof.
I can match up all the other roof vent pipes with their fixtures below, but not this one. I think it might be abandoned.
How can I determine reliably where it goes, and if it's still part of the home's plumbing system? All I can think of is to smell for sewer gases.