in Germany we use a sort of plastic jerrycan that we call "Huehnersdorf Kanister". These are made from extra-thick black plastik and are very, very strong indeed- won`t even blow up in the hot sumer sun.... They hold 22 liters of fuel. Now the trick: They also make a removable device or armature that screws on these "Kanisters" in seconds, it has a little fuelfilter at its end which reaches all the way down into the can. So in case my built-in tank gets empty, I drag one of these black bastards out of it´s storage, plug and screw the armature in it, connect it to my fuel line, pump 3 times and off I go again- this will also work in a swell when you`re not able to pour anything into a regular tank-opening no more.....