The gray water dows not flush the tank. It will flush the drain line and sewer line.
Cleaning the holding tanks? Nothing. Many folks when their done for a while will put a hose down the toilet and swirl it around. Many RVs have black tank flush, I doubt yours does so dont worry about that. At RV parts stores you can buy a short plastic device that attaches to a garden hose with many jets to help clean the black tank.
Search GEO method for ways to thoroughly cleaning the black tank. Basically it calls for 5 gallons of water a cup each of Dawn dish soap, Calgon water softener and 10 pounds of crushed ice, and driving around for a while.
The key to proper system maintenance is septic safe TP, and nothing else. No wet wipes, no sanitary pads, NOTHING! And lots of water.
Same for the gray tank.
