This has been an annoyance since cataclysm went free to the interwebs. For many items, its pretty simple to just hammer minus, and mass produce things. Liquids, however, can get annoyingly repetitive if you are filling something huge (like that wood barrel some guy left in a fridge). I noticed changes are currently being made to how water is moved around, so a better time for this there likely is not.
I propose that, when crafting liquids, if the user has > 1 unit of the required materials then a prompt shows up asking how much to make as well as which item to put it into. The crafting would then repeat the recipe with these parameters until either the desired amount is done, the container is full, or the materials/tools cease to exist.