Myth Busting Monday - Water Drains Backwards

I wanted to start Myth Busting Monday with my all time favorite myth:

Water drains backwards in the Southern Hemisphere due to the Earth's rotation

Here is one quote I found while researching this myth:

Not only is the Earth's rotation too weak to affect the direction of water flowing in a drain, tests you can easily perform in a few washrooms will show that water whirlpools both ways depending on the sinks structure, not the hemisphere. [source]

In researching this myth I found out about something called Coriolis force, here is the wikipedia entry which gives a big, long technical definition and explanation. Basically the Coriolis force is the force that one spinning object has on another object in motion; an example of the Coriolis force is the spinning earth causes tornados and hurricanes in the northern hemisphere to spin counterclockwise and clockwise in the southern hemisphere. This might lead one to think that the same effect occurs with draining water but here is a quote I found about the relating the Coriolis force to draining water:

The Coriolis force is so small, that it plays no role in determining the direction of rotation of a draining sink anymore than it does the direction of a spinning CD. [source]

Here is an explanation from snopes as to why water draining in the direction is does:

Toilets and sinks drain in the directions they do because of the way water is directed into them or pulled from them. If water enters in a swirling motion (as it does when a toilet is flushed, for example), the water will exit in that same swirling pattern; as well, most basins have irregular surfaces and are not perfectly level, factors that influence the direction in which water spirals down their drains. The configuration of taps and drains is responsible for the direction of spin given to water draining from sinks and bathtubs to a degree that overwhelms the slight influence of the Coriolis force.[source]

I have always wanted to call someone in Australia and ask if their toilet bowl flushes down clockwise or counter clockwise, but now I can avoid the huge phone bill that would result by knowing that a toilet bowl flushes a certain direction depending on how it is made.

What are your thoughts about this myth, let us know in the comments.

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