Forget about the dump lights on the stove that are always wrong for the Gray and Black tanks. Cover them with black tape. They are NOT needed IF you will always use fresh water from the tank. [Don’t connect the hose to fresh water inlet] Well, using the capacities for a mid bath made in the last 20 years, fresh water is about 60 gallons, the gray tank holds 40 gallons and the black tank just under 30. So a reasonable allocation of 60 gallons of fresh water can not fill two tanks of 40 and 30 gallons.
A couple taking a Navy shower every other day in the dry desert SW can go 5 to 7 days on 60 gallons. When the fresh water is empty it’ time to dump both tanks.
It takes us less than five minutes to dump. We use the hose stored in sewer hose tunnel. The only fitting is the bayonet one that attaches to the storage valves. The other end has nothing on it so it can fit in the tunnel. This is the way it was designed. Dump the black tank first. Then the gray tank which will wash out the black tank residue. Finish with quick rinse of fresh water, shove the hose back in the tunnel and, this is important, put about two commode bowls of fresh water in the black tank and be gone.
Don’t be like the big rig folks with sewer hoses connected like Christmas lights laying all around.