Toilets don't flush clockwise vs. counterclockwise as a result of being on one side of the equator or anotherThis fact is so ingrained into our public consciousness that even shows like The Simpsons get it spectacularly wrong, and we've almost all had teachers cite this in class while explaining the Coriolis effect. The thing is, it's balderdash. To get a sink or toilet to drain in different directions is much more a matter of drain shape, the motion of the water when the container was filled and so on. You literally need to leave a big reservoir of water sitting for days to be able to get it to behave in a manner that's observably changed by Coriolis forces, and that's after protecting it from wind, sun, vibration, etc, and using a special drain and tub.
For the most part, water doesn't care what side of the equator it is on -- it will always take the path of least resistance. Nonetheless, the myth that sinks and toilets drain in opposing directions depending on your equatorial frame of reference remains an enduring one.
When citing this, people often refer to the Coriolis force, an "artifact of the Earth's rotation" in which "projectiles traveling in the Northern Hemisphere seem to veer to the right of their intended destination," writes science education expert Michael DiSpezio. But when draining a sink in either hemisphere, the Coriolis force has no effect. The only way that you can observe this effect on water is to use a sink about a mile wide. Even then, DiSpezio writes that "the very weak Coriolis force effectively impacts the moving fluid" chiefly because the drain time is so long.
DiSpezio, Michael A. "A Different Spin on Coriolis: Applying Frame of Reference." Science Scope magazine, January 2011.
EDITOR'S NOTE: An AskMen reader adds his two cents:
The cause of water flowing in different directions is due to the Coriolis effect. On a larger scale it's much more prevalent. Think weather systems: Pressure systems rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern.
Now toilet manufacturers can design the toilet jets to create a certain flow, and I believe that it is done not to fight nature but to flow easier with nature... So an "unmoving" bowl of water will rotate in different directions, but a toilet's jets can probably overcome the Coriolis effect.
- Jay Roberts