Originally Posted by MrsChilerick
One thing we just learned, is that there are services that will "power wash" out your holding tanks and claim to bring them back to almost new condition. We've never used one, but think they might be helpful with holding tank problems.
We used one of those services All Pro Water Flow
to clean both our gray and black tanks. We were amazed at the amount of calcified crud that came out of the gray tank. Our black tank was excellent by comparison.
Although the cleaning did restore the gray tank sensor to proper operating condition, the operator was unable to get our black tank sensor to work for more than a day before it went back to its usual "100% full" readout. It doesn't really matter; we get 7+ days on our black tank so dumping it once a week works fine for us. I considered investing in the SeaLevel gauges but decided that I don't need to know the level any more precisely than I can estimate it at present.