Hopper Bucket
Allows hoppers containing buckets to remove and add fluids from the world.
Hoppers containing empty buckets will drain fluids from above them, filling the buckets.
(They will only do this if there is space in the hopper for the filled bucket.)
Hoppers containing placeable liquid buckets will place those liquids at the output of the hopper, draining the buckets.
(This also works with powdered snow.)