My Dr. Seuss plumbing is kind of funky, but it works. I don't maintain a city water connection. I could, but I'd have to leave a window open to run the hose inside the bus to hook it up. The setup could be modified to work with a through the wall fitting (and pressure control device) for continuous city water connection. (Honestly - I did it this way on purpose!)
To fill the tank.
1. Turn pump off at breaker (a switch at the pump would be nice).
2. Attach hose between Hose Bibb and city water (don't turn water on yet).
3. Open Flood Valve -- this lets water go into tank.
4. Open Hose Bibb -- this connects city water to fresh water system.
5. Turn on city water -- the tank will start to fill.
6. WATCH TANK LEVEL! Turn off city water when tank is full.
7. Close Hose Bibb -- this disconnects city water from fresh water system.
8. Close Flood Valve -- this keeps pump from circulating water through lines and back into tank.
9. Turn pump back on. Disconnect hose from Hose Bibb and city water.
Now you have a full tank! The tank is vented just by the gaps around where I cut the holes to put the draw pipe and the fill pipe in the top of the tank. If you were to have real, honest to God, fittings on a tank, you'd need some other provision for venting the tank when you fill it.
To run on city water.
1. Turn pump off at breaker (a switch at the pump would be nice).
2. Attach hose between Hose Bibb and city water (don't turn water on yet).
3. Open Flood Valve -- this lets water go into tank.
4. Open Hose Bibb -- this connects city water to fresh water system.
5. Now you are running on city water. A backflow valve on the line from the pump keeps the water from circulating back through the pump and into the tank.
I have run this way a time or two just to test it, but I do not maintain a city water connection. I fill my 40 gallon tank about every 4 days.