In 30 years of camping with three different trailers all I have ever done is wait till I am at our first camp site then:
1. make sure the plug is in the hot water tank, and make sure the low point drains are closed
2 Make sure the water heater by pass valves are NOT in the by pass position and make sure the water heater is turned off
3 Close all the faucets except leave the hot water one at the kitchen sink open
4 Attach a hose and turn it on. it will take a few minutes to fill the tank and then then it will flush any pink stuff out of the line to that faucet.
5 When the water runs out clear, shut that faucet off and open each other hot water faucet one at a time (including the shower)
6 After each one has run clear, do the same with the cold water ones and lastly flush the toilet.
We don't boon dock and don't use the water pump. If you do just do the above by putting water in your fresh water tank and use the pump
Guy