Black Tank valve failure scenarios

A few years ago we were in Hot Springs, Ark and because it was the middle of summer it was hotter than Hades so we decided to stay at the KOA which offered not only electricity so we could run the A/C but also an inviting pool. We rarely camp on sites that also offer water and sewer but in this case it was full service, whether we wanted it or not. I also very rarely ever drain the tanks with a stinky slinky, instead normally use my FloJet waste macerator, but for whatever reason I decided to try it this time. We'd been on the road for quite awhile by that time, the tanks were getting full, the sewer inlet was right there so I thought "What the heck". BAD idea :S ... I no sooner hooked up and pulled the BW waste gate when "stuff" began back flowing out the connection and all over the ground ... yikes! :E :E We called park maintenance who immediately sent around a guy with a long snake ... turns out they'd been having serious problems just like this all over the park and he spent a couple of hours trying to unplug the line. Eventually he did and I was a Happy Camper again, 'though the lingering smell never really did go away ... and I never did see that pool!