You will probably want a portable portable pump.
A cheap solution is to use a 12V marine bilge pump. They are submersible pumps, so they can be used only if the contained has a large enough opening to drop in the whole pump (they aren't big, though). The inexpensive models only lift water 5-6 feet, but that is usually enough for transfering water from a container to the RV water inlet. You will need a fairly large capacity model (e.g. 1700-2200 gph) to get enough pressure to force open the check valve in your RV's water inlet, but they can be found at a Walmart or Kmart for around $20.
A regular RV or boat fresh water pump (or a wash-deck pump) will do a better job, but expect t pay $80-$120 for the pump.
For either of these you need to find some 12V power convenient to your water fill area to power the pump and wire the positive and negative leads of the pump to the power source. Include a fuse (rated to match the pumps max amp draw) on the positive side and you will probably want to install a receptacle so you can plug and unplug the pump from the power. A simple connector such as those used for trailer lights will do the job inexpensively or you can buy something a bit more elegant at amarine parts store.
Another simple solution is to use a simple portable pump powered by an electric drill. You have 120 VAC power available in your motorhome (genset or shore power), so you can plug in the drill, connect the pump to the drill chuck and drop the suction end of the hos einto the contained.
For any of these solutions, you will need to mate a water hose coupler to the pump output line. Exactly how that is done will depend on the size of the pump outlet hose, but any hardware store should be able to supply the necessary adapters.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC