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There are videos and articles on the internet which demonstrate that water flows down a flush clockwise in Northern Hemisphere and anti-clockwise in Southern Hemisphere.
There are others which call this a total myth, and one of them is a very popular website. Link : http://science.howstuffworks.com/science-vs-myth/everyday-myths/rotation-earth-toilet-baseball2.htm
Interestingly, I got introduced to this by a Children's Fact Book. I am not quite convinced that it is a myth.
Can you suggest a way to proceed towards an analytical treatment?