Orion, your spot on for my first plan of attack. To be honest, this is our first year with the camper so for all I know it's been doing this forever. What may have not been an issue for the previous owner may have reared its head as we hook up to facilities at our seasonal site so the sewer remains open to drain dry. I expect this is why the problem just showed up as if the tank held any water I doubt it would heat it up enough to melt it. When I pulled the fuse and it didn't shut off I was kind of baffled, so I sat back and poured a whiskey and thought about it for a while, lol.