The Jetpack Fueller is used to fill the Jetpack (not electric) with Fuel. The Jetpack can be anywhere in your inventory, including on your back, and you must be holding the Fueller in your hand. Right click on a Tank with Fuel in it and your Jetpack will be instantly refilled, using about 1/4 of a bucket of Fuel.
Note that it cannot be powered with Oil.
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