I see what your talking about in this diagram. It looks like most of the stuff in the house is hooked up to what I think is the secondary vent line. The only vents I cant find on drain lines are the kitchen sink drain line, and the tub, it has that over flow piping but no vent beyond that. All of this is exposed under the main floor in the basement so its easy to see.
The only thing I can't physically see is where the secondary vent line goes into the main floor. I can see it connected to the drain lines for the shower, toilet, sink in the basement, then it T-s up into the unknown. A wall in the main floor bathroom. Where it connects to the main vent stack is the mystery or if at all. Part of me is wondering if they shoved that pvc line up into the roof space.
You can see the main vent line in the basement and all the connections are from drains coming from upstairs. I can only see so far up the narrow channel into the first floor and into the roof space and eventually the roof vent cap. It might be connected farther up in the wall somewhere.
But yeah there is no vent line on my washer setup your right. I am half wondering if I should cut a line into it, and change the Y to a T. It seems simple enough to do with the drop ceiling. Really easy actually
The T connection in that diagram for the laundry and wash basin is exactly what you are talking about. For discussion sake it serves the same visual as my washer and sump pump setup into the basement drain.
Now is that the only floor drain in my basement well that I am unsure. The only one I can physically see anyway other than the sump hole. There could be another one hiding under that flooring somewhere perhaps, but that is not important in regards to venting so much as flooding.
Edit: Added this picture for educational purposes
Edited by FLASHINGROOSTER, 09 August 2021 - 03:07 PM.