HI all.. it's been quite a while since I have been here... Nice to see that everyone is still busy with plumbing projects. While working on putting our new shower in it came to my attention that my MIL ( who lives with us in her own place that is within ours) does not have ANY venting of her plumbing.. I have looked and looked and there is not one. The thing is.. the system works, her shower drains, her toilet flushes and her sink drains.... so uhhhh not to dump over the apple cart.. but..WHY is it working?

My fear is that there is an open vent in the wall ( it would be JUST like the guy who use to own this place).. so while this is not an issue right now since it's all working I would like to get ready to address this since the bathroom I am working on is right above hers I want to add a vent line ( my bathroom happens to have two) or more to a point a way to tie into those lines when the time comes. Not to be morbid but she is living in what will be our master suite and is near 90 so after she passes we will take back over that 1200 ft of the house with a total redo ( rip out her kitchen put in a big bathroom etc)... and at that point I want to have a the plumbing vented if in fact it's not right now. Thoughts? suggestions???? Can the system really be working with no vents???