We use Happy Camper after every dump when boondocking and every second dump when hooked up to water. We always flush black tank well and have no problems with it. The question I have is the grey tanks. Sensors do not read properly on them. We have been trying various methods that are out there, ie borax etc. Not much success. Is there a way to flush the grey tanks?

I don't use them.

Not a full-timer but a boondocker, and I use Happy Camper and Borax in the black tank after each dump and the gray tanks as needed.

Guess we're in the 10% of the poll (above) that don't find a reason to treat either grey or black. However, we are occasional users of our trailer, not full timers. One thing we did that's been helpful was to measure what each LED light on the tank panel is actually measuring for each tank: grey, black and fresh. Very enlightening since the sensors were not as accurately placed as one would hope. Also, no toilet tissue goes in our black tank. For those who've traveled extensively, you'll know that its very common in older cities/towns (e.g. in Europe, N Africa, Pacific islands) for tissue to be placed in a covered container beside the toilet. I realize some find this gross (or worse) but it strikes us as a reasonable alternative and we've never experienced any odor in the trailer's bathroom.

LOL! The folks who never use toilet deodorants and claim to never have had problems with smells probably lost their sense of smell due to covid. :-)

We've used Happy Campers product for the past, almost, 2 years in our stationary 5th wheel. I like the no-smell and no-scent results. We also use it in our truck camper. I've recently discovered that the price on Amazon Canada has greatly increased and that the Canadian supplier from Alberta no longer is a dealer. They are selling and packaging their own label product now. Has anyone tried it? It's called Classic Campers.