Is it true that a toilet flush will rotate clockwise in the northern hemisphere and counter clockwise in the southern hemisphere? If you watch the cartoon network you may see an example of this. However this is simply a myth. The equator has no effect on a toilet flush and its direction of rotation. The design and shape of the toilet bowl itself will determine the rotation of the water as it goes down the drain.
The myth that water will spin down the drain in opposite directions depending on the hemisphere you happen to be in, was likely perpetuated by a force known as the Coriolis Effect. While the Coriolis Effect has no influence on your toilet bowl, it is a very real phenomenon that would influence something much larger than your toilet, like say for example a 500 mile wide cyclone.
So without getting too scientific on you, here is how the Coriolis Effect would influence the cyclone. Let’s say that a strong wind was blowing due north towards the North Pole. Now since the earth is rotating towards the east, there is strong force trying to move the wind off course. Since the earth is round, the closer you get to the North Pole the lower the speed of this opposing force. The effect would be that the wind moving north would veer off to the east, thus creating a clockwise rotation, or the appearance thereof. Of course the opposite would be true if the cyclone were below the equator. Oddly enough, there would be no effect on something situated directly over equator itself.
The French scientist Gaspard-Gustave Coriolis published a paper on the Coriolis Effect in 1835, hence the name. While he wasn’t the first to recognize the effect, his work did lead to the common use of the term in meteorology. Watch your local weather channel and you may just hear this phase pop up from time to time.
So now that your head is spinning more than the drain, let’s get back to the toilet flush rotation. With a general understanding of the Coriolis Effect it is easy to surmise that your 16 inch wide toilet bowl is far too small to be affected by the curvature of the earth. Now if you were to build a toilet that was 500 miles across, perhaps we could see the Coriolis Effect in action. The problem is you could never find a bidet toilet seat large enough to match your 500 mile wide toilet.