Way back in the days of old (before built-in black tank cleaners), I was at a Coachman club campout. I always liked to attend these as a good place to learn from others.
My camping neighbor had a wand that he put into the tank through the toilet. It had a jet sprayer on it, and you could spin it around to clean the side walls of your black tanks.
It sounded like a good idea to me so I borrowed it to clean out my tank before we disconnected to go home.
I very diligently cleaned the tank for all that I was worth. I am sure that I missed no nook or cranny. Then I went outside and pulled the handle.
You would not believe how much poo and paper exited. It blew the connection apart right at the valve, and I could not close the valve fast enough to prevent many gallons of goo from blowing out of the severed connection.
I don’t think there was anything left in the tank. It was all over the lawn.
The cleanup took quite a while and drew quite an audience.
David Webster, Fifth-Wheel