My sequence is
Isolate water heater tank.
Add suction hose by water pump and change the valve there to the hose. put hose in pink fluid.
Back inside, turn on pump. Open cold tap closest to water heater (Kitchen sink for me) and run until pink flows. Repeat with cold tap.
Do other taps -- shower, bathroom sink, toilet.
Go outside and drain black and gray tanks. Close drains.
Add a bit of pink to all the drains, just to make sure.
Drain Fresh water tank. Take off suction hose and change valve.
Drain water heater.
You will have to change the bottle of pink once or twice during this.
David and Dayle