Besides using a Flush King for backwards flushing the tanks on a regular basis, I used to open the sliding panel in the front bay near the drivers side and located the waste drain pipe that was capped off right behind the door. Removed that cap and run a cut off piece of hose down that pipe a few feet and turn on the hose to blast water in to that pipe and then into the grey tank. Had to use a rag to seal off the end around the hose so no water would spray/leak back out when flushing. Be surprised what was hanging on the inside of that gray tank. I would do that when the gauges were reading wrong, helped a lot. So maybe every 4 to 6 months this was done. Normally waited till we were in a park with really good water pressure.
2018 Holiday Rambler Admiral 31A
2015 Cadillac SRX (towed)
2019 Tesla Model X
1991 Avanti Conv