In this video, I disassemble my RV waste tank sewer plumbing and remove the black tank valve for inspection. For the last while, the black tank electric valve hasn’t been fully closing.
Once I get the system apart, the problem is self-evident. I found a wad of toilet paper with what looked like sawdust jammed in the lower portion of the wastegate preventing closure.
I removed the obstruction and cleaned the electric valve and rubber o-ring seals, reassembled. Everything is back working well.