Would be mindful that gasoline dissolves many types of plastics, some faster than others. For example, a plastic milk carton filled with gasoline might hold for a few hours before failing.
Some fuel tanks (such as found on lawnmowers) and gasoline spare "cans" are of course produced from some sort of gasoline proof plastic.
Rumor has it that some of the newer gasoline blends will gradually eat through the older fiberglass motorcycle fuel tanks designed to contain the older gasoline blends.
Without knowing much about the many different plastics or which non-gasoline containers might be relatively gasoline-proof, I prefer using a known gasoline-proof container such as an old lawnmower fuel tank as the alternative fuel suppy for running the engine with fuel tank removed.
An on-off valve in the fuel line from the temporary container is cheap and easy.
That said, the Roundup container may do perfectly well for the short time involved, but I wouldn't leave any residual gasoline inside it when finished.
Then there's always the professional model available.
Good Luck!