The water in your sink does not care which hemisphere it is in. The Earth’s spin does push on it, but at that size the push is millions of times weaker than gravity, and the way the basin was filled, the swirl your hand left, the shape of the bowl, all win easily. In 1962 Ascher Shapiro at MIT set out to see it anyway. He filled a wide tank, covered it, and left it alone for about a day so that every stir from the filling could die away, then opened the drain. For twelve minutes or so nothing turned. Then the water began to circle, slowly, counterclockwise, the way the Northern Hemisphere says it should. A team in Sydney repeated it a few years later and got clockwise. So the story everyone tells about the plughole is true, on one condition: that nobody has touched the water since yesterday.