Onboard water system pumps water out the shore input

Or, if you are really in a hurry you can go to a hardware or big box store, buy a ball valve and the adapters and nipples needed to accept the male fresh water hose(female hose pipe interface) and a male hose fitting to plug into the coach city water supply.

Ball valve on when connected to city water, off when you want to use the on board fresh water.

Just did a 10 day trip and did not have to use the spare!

Bought the parts, the glue and made 2.

Works like a charm and I think I spent about $12.