City water is pressurized water--it doesn't fill the tank, its just a direct connection to the plumbing. Typically you'll want a regulator here, especially if you're in a larger park with high pressure water.
Like this guy:
Hi Flow Water Regulator - Lead Free - Valterra A01-1122VP - Faucets & Inlets - Camping World
I put it on right at the spigot so that it also protects the hose.
The water fill on the passenger side fills the tank (and thus you have to turn the pump on for it to work).
If you are going to be camping with a water hook-up then only fill the water tank about 1/3 full (enough to use the bathroom & wash your hands en-route). Then when you get there turn off the pump and hook up the city water.
If you are going dry camping fill the water tank full before you leave (if there is no fresh water available at the campground--if fresh is available then do the above: fill 1/3 or so then top off at the campground).
No sense carrying extra water (extra water = extra weight).
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