I have a second floor bathroom that has the typical tub, toilet and sink. Problem is there is no vent that I can see and the tub won't drain unless the toilet outake pipe is open (toilets removed). Sink seems OK, toilet and tub drain within a foot into the same line the sink is about 6 feet away and ties into the same drain line. So, it goes tub drain, tie in sink drain, tie in toilet drain (smaller pipe 1 1/2 brass I think for tub and sink-- and 3 inch PVC for toilet for sure) emptying into 4 inch PVC to CI.
Can I use an AAV to solve this problem? If so where do I tie it in after all the tie ins? My thought was to put it in the 3" pipe with a T-y; 1 1/2 inch vent.
Suggestions?
Thanks

