If you have watched the movie "RV" with Robin Williams, you will recognize it is a documentary, not a comedy!
Years ago, with a brand new class c MH on vacation, the black tank wouldn't drain. I poked sticks up the hole, bought a snake to run through it, and even stuck my arm down the hole. No luck...until I felt something move while using the snake. While looking up the hose, I poked more energetically with the snake. Out pops a circular plastic disc from when they cut the hole for the tank inlet...followed by a full black tank's worth of "material"! I got it into the sewer hole, but not until I got a good dose of it. Needless to say, I used the outdoor shower to clean up followed by a change of clothes.
I'm a little smarter now.