Water pump mod question

[Riwright]

There are some good threads that involve filling the camper while closed. There are others that describe installing a second water pump that is used to draw water from water jugs into the fresh water tank.

I would like to do mod that combines both functions.

I am looking at putting a city water inlet on the bottom of the camper. This would run to a second water pump and then to the fresh water fill hose. The pump would be switched.

For an unpressurized source such as a water jug I would attach a hose to the city water inlet, put it in the jug and turn on the pump.

My question has to do with operation with a pressurized source. I don't think that turning on the pump and sucking water out of the spigot would be a good idea. But would the pump allow the water to flow through when it wasn't turned on? I suppose it would just spin as the water went by but I'm not sure it would work this way.