We only use the Newell for a week or two at a time. I have never hooked the city water up. I do as Russ suggested. I'm running two 12V pumps in tandem. It runs the shower and dishwasher fine. You can tell when you draw water while the toilet is filling etc. But for our limited use it has worked well.
The one disadvantage I noticed for just topping off is that I cannot close the bay door while a hose is connected to the top off port. Which would make it easier if I was staying for a week or so somewhere with full hookups and just use the hydrant valve to fill after dumping.
It is not necessary to "top off" using the top mounted port. Just configure your valves for filling via the city port and run the hose as you normally would through the hole in the floor, just turn on the city water to fill. As my daughter would say, "easy peasy".
We always use a regulator when hooking to city water. They are pretty cheap at Camping World.