Q: I've been told that water goes down a sink in one direction in the Northern Hemisphere and in the opposite direction in the Southern Hemisphere. Is that true?More here.
A: No! The origin of this myth comes from applying a scientific principle to a situation where it does not fit. The Coriolis deflection causes cyclonic systems to rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. It was inevitable that someone would suggest (without checking) that a sink should drain in a similar manner.
However, a cyclone is more than 1000 kilometers in diameter and may exist for several days. By contrast, a typical sink is less than a meter in diameter and drains in a matter of seconds. On this scale, the Coriolis force is miniscule. Therefore, the shape of the sink and how level it is has more to do with the direction of water flow than the Coriolis force.
h/t Marc for asking.