We have a small utility trailer with a couple of 55 gallon drums on it we use for collecting. We built a simple wooden "cage" out of 2x4's to secure the barrels After messing around with a 12v pump, believe it or not we went with a high volume hand crank rotary pump. It's mounted on the side of the wooden frame holding the barrels.

Harbor Freight, about $50.
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It moves up to 25 gpm, and guess what, it really does move that much with very little cranking effort. It uses standard sized plastic flex hose, so we got a long length of pool vac hose to reach the WVO storage barrels at our sites. It literally takes 3-4 minutes to completely drain a full barrel without breaking a sweat on the hand crank. We've got a short piece of hose for going into either of the barrels on the trailer.

And another nice feature: it's reversible, so when we arrive at our storage facility, we can drop the short hose in the trailer barrels, and run the long hose into our storage barrels in the building. About 6-8 minutes of cranking and we've unloaded both trailers barrels.

No batteries to worry about, pumps breaking down, etc. I would have NEVER thought we'd be using a hand crank pump, but it's da bomb!

TX