Or....you could rig up something like the electric transfer pump I use. Just stick the nozzle in the fuel tank, turn on the pump and watch the fuel level slowly rise to the desired quantity in the calibrated sight gauge on the fuel tank.
The pump is a Carter automotive/marine pump that delivers ~1 gal/min. It is powered by a 12v battey that has been retired from aircraft duty. The five-gallon fuel can sits on the plywood platform.