my solution that has worked very well
1) buy the 6 gallon square blue water jugs that have a vent hole and a big threaded spout
2) get some 1/4" SS tubing long enough to go to the bottom of the jug. Cut one end at a 30 degree angle or so and put flexible hose on the other end.
3) ream out the vent hole to just large enough to let you push the SS tube through it.
4) Then I added a RV water pump in my pass through near the water inlet and connected it to power with a switch.
5) I connected the other end of the tubing to the water pump inlet
6) I spliced in some tubing from the output of the water pump into the water inlet big flexible tubing.
Now to fill from the external jugs, I put them on the ground, stuff the SS tube into the jug vent hole take off turn on the water pump and let it pump away.
If it isn't easy to plumb directly into the water inlet, just run a hose from the pump outlet that is long enough to fit into the water inlet to the RV fresh water tank, insert it before you start pumping.