I think its rather tedious to fill all buckets in a cupboard with liquids from a barrel one by one (or two by two, you get the drill).
The solutions i propose are :
-make the barrels interactable just like a cupboard, so you can craft directly from it by just opening a barrel (or having it in a garden shed, but what do i know).
or
-fill all empty buckets in the cupboard, when the user lifts the barrel and right clicks the cupboard.
This small change can be a great convenience improvement.