Thanks at all,
Unfortunately, I can install natural vent only near the inspection point, so near the end of the plumbing.
maybe I could intercept the main pipe just before it enters the inspection point (immediately after leaving home), and start the natural vent pipe from there, but I can't understand how to start it 15-20'' later, directly from inside the inspection point can make a difference in operation.
what do you think about this? (in my ignorance, I have always seen the inspection point as if it were a simple "inspectable joint" of the pipe)
From your advice I understood that the best point for natural vent is near the toilet in bathroom 2 (highest point of the plumbing),
but unfortunately now I can no longer do this thing.
at this point I am undecided on what to do and I don't know if it is worth inserting a natural vent near the end of the plumbing, since it will not work well? in this situation I can only put AAVs on the sinks in case of future problems?
Very Very Very thanks