Do you know what this thing is, next to the main waste pipe? It looks like some sort of access port or perhaps a check valve? It was covered with mold like stuff. There’s also a sump pump right next to it (out of the picture). Sorry pictures aren’t the greatest.
Thanks for any advice!
It looks like an expandable plug in there.
This type of thing: (Probably trying to stop a back up.)
Correct. It is a test plug. Basically a way to plug the line. Usually they are just for testing inspection purposes. However people use them as an inexpensive way to cap a unused line. Who knows, where it goes? You may have to ask some questions if possible. If it has mold around it and is nasty, you may not want to take it out and see what is behind it. HOPE THAT HELPS.
Ok thanks Larry and Jonathon. That makes sense. The waste pipes did not have a cleanout/access from the basement. Perhaps that was installed to be able to inspect/cleanout/scope/etc… the waste pipe out to the street.