I am new here and hope to get help.
Some years ago an amateur plumber installed a new toilet in my basement and he did not install a vent. The toilet did not flush, and I installed an air admittance valve, as illustrated in the following drawing.
I assume nobody did this, but it worked, until recently. I took away the aav, and it flushed very well. I bought a new aav, and put it there, but it did not flush.
I added another aav below the sink, which is just two feet away from the toilet, but it did not help. The aav won't help the toilet to flush.
I wonder what the problem or problems are. Why the old aav worked and now it stopped working? I took away the aav, old or new, it flushed perfectly. I also do not understand why the newly added aav does not help.
I would like to know how to solve the problem.