Our C has no gravity fill either. I miss gravity fill. Simple.
We have to put our valving in certain positions (no need telling you ours -- it will be different on yours) and it will SUCK the water from a container (water w/o pressure). So, for the hand pump at the Forest Service campsite, pump it into a bucket/clean water storage container, and run a hose from it to your water input....AND place your valving in the right position. Check owners manual or see your dealer.