That gas pump thingy seems kind of overkill for just filling a gas can from your car. It looks intended to pump liquids uphill, or maybe to pump gas from one car to another.

For pumping gas out of a tank into a can that's lower than the tank, I remember getting a siphon pump at the hardware store for $5 or so. It was just a piece of plastic tubing that had a squeeze bulb at the end with a flapper valve inside. Squeezing the bulb was the equivalent of sucking on the hose. You'd just give it a few squeezes and gas would start flowing. The whole thing weighed just a few ounces and there was not much of anything that could go wrong with it. I guess you could even pump uphill by keeping on squeezing, but it would be tedious.