Yes. If the sink drain is without a stopper, you should me able to shine a light down the trap and see if it is full.
When the waste exits the P-trap of the sink, and before it starts to go down, there must be a pipe coming off that arm within 42" for the size pipe you are using that goes up to act as the vent. Since it looks like the sink's drain just goes straight down in the wall, there MUST be a vent line going straight up from where it transitions from horizontal to vertical off the trap arm behind the P-trap, or it is an S-trap. Depending on the flow, you may or may not be able to siphon the trap in the sink, so the test is not definitive.
Some places allow an AAV, some don't. Having one is better than an S-trap. They can and do fail eventually, so they must be placed where they can be accessed. You want is as high in the cabinet as you can reasonably get it and still unscrew it to replace it.
You don't really want to keep it into the toilet fitting, but I don't think it really matters which other choice you make once you've got the sink vented.
I'm still wondering why you don't just vent the sink and cut the sink drain wye into the toilet waste arm, downstream of the closet bend?
The "You don't really want to keep it into the toilet fitting" part made it sound to me like putting the wye after the elbow or "toilet waste arm" was not the best way to do it. :confused:
The issue is the existing closet bend with the heel inlet. Getting rid of that and cutting in the wye is fine- as long as the sink is properly vented. If it is not vented, the sink's trap can get siphoned every time you flush the toilet.
So the advice of a working plumber is not good, but Jim the Retired Defense Industry Engineer's is.Quote:
Because Jim said "You don't really want to keep it into the toilet fitting
I can't tell you how many thousands of jobs I've had permitted and passed. :)
I forgot to ask. I've read that there are cheap AAVs to avoid. What would be some brands/models that have a good track record?