What is the fastest way to empty a full jug of water: tipped upside down or poured at a particular angle?
The quickest way to empty any cylindrical vessel without an aid is to tip it upside down and swirl it around rapidly. The induced vortex will create an air channel right up the middle to the bottom of the vessel. This lets air behind the water and so the whole mass of water is now free to fall under gravity. Without swirling to let air pressure in behind the water, it is held back because it begins to produce a vacuum as it falls, which pulls in the opposite direction to gravity. This wouldn’t work in microgravity and is highly discouraged in the space station!
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