I have removed the drain cover to find 2 pipes--one in the center that the Paramount cover (model MDX-2.5") fits into & one above it. The one above it appears to be filled with a very fine black mud-like substance. What is this pipe for? Please see attached PIC.
Thanks Mark for the reply!! I do understand why there exists a pressure relief because I previously watched a UTube video on this subject. In that video, the tech used a 1" square wrench with a 2' extender to remove a pipe plug from the drain--if you look closely at the PIC I supplied, that same type of plug is BELOW the center hole. So what is its purpose?