We occasionally camp at a location with no water. Since it's about a 3 hour drive, we try not to travel with the tanks full. To solve the problem, I bought a High Country Half Moon Lay Down Water Caddy that fits in the back of the truck. It came with a standard garden hose bib, and a shut-off valve. They come in other designs, as well. Here's a link to their website:
High Country Plastics — Home
With the tank, I can drop the trailer at the site, and drive to the nearest water source and fill the water caddy. To transfer the water from the caddy to the trailer, I bought a 12V utility pump from Harbor Freight Tools. (About $32.00 + tax, with a 20% off coupon.) Here's the link:
12 Volt Marine Utility Water Pump
I mounted the pump to a small piece of wood, and cut the alligator clip wiring off. I then added a fuse, switch and long pigtail w/connector. I added the same connector to the alligator clip wiring. I then purchased a 7-pin male trailer connector and wired a pigtail to it.
Now, with the caddy in the back of the truck, and full, I just hook a hose to the bib and the pump, and run a hose to the trailer (with my inline filter, of course). I plug the pump into the trailer connector on the truck and turn it on. In a few minutes, the trailer is full.
Here's a pic the caddy (stock photo) and the pump assembly...