Water pump for water barrel...

I used to use a 45 gallon barrel and now have a 50 gallon container(agriculture) that goes in the bed in front of the 5th wheel and fits under the tonneau cover when not towing.There is a tap installed on the bottom end of the container. I also have a 45 gallon collapsible container(from Camping World) and that goes behind the 5th wheel cross ways with a furniture blanket under it so it doesn't get damaged by whatever gets in the bed of the truck. We use it because we also camp off the grid a lot. I used to use my air compressor with the 45 gallon barrel to move the water from it to the 5er but now use a 12 volt pump. It works very well and is a lot faster than air pressure.I tried gravity feeding it but can't always get the tank higher than the fill. I had to rig up a double female, end hose to go from the container to the pump. My three kids also use a 12 volt pump to transfer water. They all have the collapsible containers. I found a plug http://www.princessauto.com/pal/en/Other/7-pin-Trailer-Plug/8462558.p that goes into the rear receptacle of the truck and I put plug ends onto the wiring of the pump and a cigarette lighter end which plugs into the receptacle of the truck. No more long extensions to get 12 volts.