“Toilets flush in the opposite direction in the Southern Hemisphere.”

The idea that toilets flush in opposite directions in the Northern and Southern Hemispheres is a widely circulated myth, often attributed to the Coriolis effect. This misconception likely stems from a misunderstanding of how the Coriolis effect works and its scale of influence. It's a popular "scientific" tidbit that has been reinforced by pop culture, including television shows and movies, leading many to believe it as fact. Travelers are sometimes even shown rigged demonstrations near the equator, further perpetuating the illusion.

In reality, the Coriolis effect is a genuine scientific principle that influences large-scale phenomena like ocean currents and weather patterns, such as hurricanes and cyclones, causing them to rotate in opposite directions in different hemispheres. However, this force is far too weak to affect small bodies of water, like those found in a toilet bowl, sink, or bathtub. The Earth's rotation, which causes the Coriolis effect, is simply not strong enough to overcome other dominant factors in a small basin.

The direction a toilet flushes is primarily determined by the design of the toilet itself, specifically the angle of the water jets that introduce water into the bowl. These jets create an initial swirl, which is the main force dictating the water's rotation. Other factors, such as the shape of the bowl, imperfections in its surface, or even existing currents in the water, have a far greater impact than the minuscule influence of the Coriolis force. While it is technically possible to observe the Coriolis effect on a small scale under extremely controlled, undisturbed conditions (like a perfectly still basin of water draining very slowly), these conditions are never met in a typical household toilet.