I don't get the mean spirited comments either. Contribute positive comments or move on.
I like the camera idea. I think I'll try it with my mother-in-laws iPhone.:)
Camping World sells a flexible tank cleaner that connects to a garden hose that has nozzles at various angles. You run a garden hose thru the window and spray the walls with the valve open. You can buy a flex hose for your power washer too. Made for cleaning gutters.
About once a year I run the flex spray up from the dump valve after I am sure the tank is very clean.
Go ahead, say mean things.
There is a nationwide franchise operation called All Pro Water Flo that has a tank cleaning process using a specially designed high pressure washer with a multi head sprayer they slide in through the valve with a camera. It blasts all the minerals that build up on the sensors. I saw them do an RV once and was surprised by how much stuff came out of the gray tank.