A concept worth flushing

Everyone knows that the water in a toilet bowl flows in the opposite direction if you cross the equator ~ or does it? Charlatans in equatorial countries have been using this notion for years to make a fast buck and dazzle visitors. With a tour group in tow, they carry a bowl with a drain across the equator and demonstrate how the water flow changes. They may be good salespeople, but they're contradicted by the Coriolis force. This effect of the rotating Earth is what makes low-pressure systems spin counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. But the Coriolis force is most evident on large-scale circulations like hurricanes and winter storms. The smaller a system, the less time and distance there is for the flow to change direction. Dust devils – typically only a few metres across – rotate in either direction in both hemispheres, and even some tornadoes rotate contrary to what you'd expect within a given hemisphere. Unless the water in a toilet bowl has days to drain, Coriolis won't make it spin any differently. The flow after a flush is far more dependent on the shape of the bowl, how the water enters, and other such factors. Moreover, the Coriolis force is strongest at the poles and weakest at the equator; hurricanes never form at 0° because they can't rotate there.