Hmmm, an interesting problem. Well, just brain storming, or maybe brain sprinkle in my case. Here some possible ideas.
1. Siphon: As long as the bottom of the water tank is higher then the fill inlet of the Hi-Lo, then you could siphon the water into it. Siphon - Wikipedia, the free encyclopedia
2. Hand pump: They make a variety of hand operated water pumps. Since your Hi-Lo is mostly in the same spot, you could go for something more efficient and a bit less portable then this model, but you get the idea. Hand Pump
3. Electric pump: I found several electric pumps on the web, but one pump that we know works well is an RV water pump. I couldn't figure out how to easily use the one in the camper for this. However, you could buy another pump, bolt it to a board, or make a fancy carry box etc. Add a couple of hoses, one for inlet and outlet. Add a couple of wires with alligator clamps to connect to the battery, and voila!