I have two bathrooms, but only see one vent pipe and it's in my attic. The first bath is on the ground level in the single-story part of the house. The second is in the second story. I found a PVC vent pipe in the attic I assume is for the plumbing. It terminates into the attic. I don't see any for the ground floor bath.

What do I have to do to be sure everything is done correctly? How do I tell if the one in the attic is even a plumbing vent and not just an exhaust vent for a fan no longer there?

Should there be only one plumbing vent for the house or one per section? I don't think the one in the attic is exhaust from a fan. Just poked my head up there and there wasn't an exhaust fan - it's a. 1/2 bath. I did find a bare wire. Great, huh. Now to figure out if it's live.

Vents can be, and often are combined in the walls or attic.
A bathroom group will usually have at least a 2" vent- minimum size for a toilet.
Older homes will have a 4" vent behind the toilet the rises straight up.
No plumbing vent should terminate in the attic though. They must go through the roof.
That pipe could even be a passive radon vent.
Consider renting a sewer camera and dropping it down the pipe.
Maybe run an electricians fish tape down it and see if comes out your exhaust fan?

The pipe I do have is a very long distance from the pipe I have. The pipe is to the 1/2 bath in the upstairs. It's a 3.25" PVC pipe and I can look down it and see a little water. I assume that's the vent to the upstairs toilet and will extend it through the 2nd floor roof.

As for the primary bath, how do I find out if there is a vent pipe at all? The house is from the 1870s. I have a drop ceiling in the bathroom and could cut into the wall above that and above the toilet if need be. It wouldn't just terminate in the wall, would it? If there is none, what do I need to do? I'm competent and have worked with plumbing before, but never with these vent tubes.

I don't understand the first sentence..
I'm surprised you have standing water in the pipe since plumbing pipes are graded to drain and 3.25" is not a standard plumbing pipe size- more like 3.5 OD unless it's thin wall PVC which has been used for exhaust fans
I didn't know they had indoor plumbing in 1870's :eek: If it's close to that age it's probably not vented at all.
If everything works fine do you want to go to the trouble to vent it to modern code? Then again, the system may be ready to fail if its 140 yrs. old. Maybe a repipe is in order? Drains and water

Oof, sorry about that first sentence. Was suppose to read that the pipe I have is a very long distance from the main bathroom on the first floor.

I assume the house did not have indoor plumbing when built and it's been redone. The drain pipes are all PVC, so they aren't ancient.

If I don't need a vent on the primary bathroom, I guess I'll just wait until I redo that bath, which has to happen someday anyway. Should I make sure there isn't a vent pipe hanging out in the wall somewhere? I need to tear into something anyway as the exhaust fan terminates somewhere in the roof, which has no attic or second story. Ugh.

As for the 3.25" pipe, it's a thin wall PVC and when I look down it I can see water reflecting but it may just be wet, not standing. The water I see is not the width of the diameter of the pipe. Sounds like a vent pipe, right? Should I have someone flush the toilet while I'm up there and see water rushes by? I should extend that outside the house if so, right?

Thank you very much for your help.

I have one vent pipe serving two bathrooms. However there his and her bathrooms with a wall inbetween.