Comment to OP:
Great info above.
One comment I saw repeated was how to insure you don't overpressure the system - if you choose air.
I made a simple fitting with Lowe's parts.
One end is a compressor fitting.
One end is a waterhose fitting.
One end has a pressure gauge.
There is a ball valve between the air ftg / pressure gauge and the water hose fitting so I can turn pressure on and off at the RV without having to hook or unhook anything.
I set the compressor pressure, hook to fitting with valve closed, hook up water hose from fitting to city water supply, confirm the pressure is safe and let her rip.
I understand compressors have a gauge also so this is redundant, but I had a compressor gauge go out once and the added safety to protect the system is worth it to me.
Best of luck
John and Caren, Arkansas. 2006 Newmar Cypress 5th wheel. "Fractured Fairy tails"