Another quick tip, before I forget … though I don’t know how I could. They say the sense of smell is the strongest trigger for recollection.
The biggest stink we ever smelled coming out of our RV holding tanks was not from the black water. Our kitchen grey water tank started expressing itself with a very pungent sulfur smell when we were staying at Lindenwood City Park back in Fargo, ND.
The lower campground had recently been re-opened after major flooding from the Red River, and a couple fellow campers said they wouldn’t be surprised if it was the water so we left it at that. When we dumped the tanks, however, we knew it had to be something more.