It's meant for stuff that uses a bucket of some liquid in the recipe. You make the recipe as normal using a filled bucket of whatever liquid you need, pump in the liquid, then make sure there's materials in the bit below to make it. After that it's a simple matter of applying a redstone pulse. A Pressure Plate right in front of it does the trick.
Then it'll make one, refilling the bucket from the tank and resupplying itself if it can from the stock below. Rinse and repeat.