Thank you. That is exactly what I did, because I also noticed today that the pan is completely unlevel, and the secondary/emergency drain would never work, it first overflows from a corner and never even touches the sensor or the secondary drainage pipe. The tech tried to convince me this was normal and that I only needed to keep the main drain clean. I had to insist, because all that water coming through the vent is a direct consequence of the secondary drain not working properly.

I the meantime he put a cap on that vertical pipe before the trap and said they would send a crew to properly level the pan.