Saw this inside the utility room of a third floor condo. The only thing visible draining into it is the Air Handler condensate. Being on the third floor it goes straight down and I presume services the lower two units. Have no idea if anything else drains into the stack. My question is since this is the top of the stack regardless of what is going into it , should it not have a mechanical vent cap?
If it goes to a sewer it should have an air admittance valve at minimum. As you have no idea if it does, would probably be a good idea to recommend evaluation by plumber.
Thanks, kind of what I was thinking but wanted a second opinion