I managed to do this recently and have been trying to figure out what I did. I meant to write it down in a notebook in-game, but I know for a FACT that I did this, because it allowed me to take cans with ~25 gas each and put the fuel all into one. You don't lose the cans this way, either. I'm currently trying to find the way I did this again. It is not a crafting recipe or the like. It's some key combo while holding one canister and aiming at another