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Here is a way to clean sensors off in black tank fill tank about half way.... get two BIG bags of ice.... Drive!

The ice will clean the inside then melt and drain fine!

Faulty sensors aren't a problem if you use plenty of water, Happy Campers and keep your dump valves closed till the tank is at lease 2/3 full. You can get Happy Campers treatment at finer RV supply stores or online at several vendors. Here's a link to one on Amazon: https://www.amazon.com/Happy-Campers-Or ... 005XEFADU/
At the end of each outing, I triple flush my tanks using the built-in sprayer and add a few gallons of fresh water after closing the dump valve. Then add Happy Campers treatment to the tank so it sloshes around on the way home and back out the next trip. My 16 year old sensors still work great.