A Jayco Exp is a separate model line 19' to 29'
A Jayco LGT is a separate model line 25' to 31'
A Jayco Ex-port is a separate model line and is ONLY a 17C
A Jayco Sport is a separate model line 16' to 21'
So I take it you have a Ex-port 17C........
That rig uses a gravity port to fill fresh water tank.
So without city water connected you just turn on the on-board pump, open a faucet to bleed air & prime pump.
Leave faucet open until pump primes and water flows.
Pump is an 'on demand' pump......runs when faucet is open and then shuts off after faucet closed and line pressure is restored (standard pump starts 30# and shuts off 45#)
City water and pump discharge feed same cold water plumbing lines. Cold water then feeds water heater for hot water plumbing lines.
No valving to swap when using one or other
Water heater has a 'bypass' valve (and cold water inlet) to isolate water heater. (6 gallon water heater)
24.5 gallon fresh water tank (30.5 published includes water heater)
Here is how a BASIC GENERIC RV water system is plumbed
