Do Toilets Flush Backwards in Australia? The Real Answer

No. A toilet swirls the way its design tells it to, in either hemisphere.

Where the idea spread

The Simpsons episode "Bart vs. Australia" (Fox, 19 February 1995) has Bart phone Australia to check which way a drain spins. The show blamed the Coriolis effect, and plenty of people have repeated the idea since. It was around before the episode, but the show made it famous.

What the Coriolis effect really does

The effect is real. Earth's spin deflects moving air and water, and it sets the direction of hurricanes: counterclockwise in the north, clockwise in the south. But it acts over days and hundreds of kilometres. In a toilet bowl, where the water moves for seconds, it is far too weak to matter.

What decides the swirl

The angled jets under the rim push the water round. The shape of the bowl and any leftover motion from filling it also count. All of these beat the Coriolis effect by a wide margin.

The one time it showed up

In 1962 Ascher Shapiro at MIT filled a bathtub-sized tank, left it still for a day, then drained it slowly. It turned counterclockwise. In 1965 a team at the University of Sydney repeated it and saw clockwise. Both results were published in Nature.

So the myth is true if your toilet is a bathtub and you wait a day to flush.

Sources

• Scientific American, "Does Water Flowing down a Drain Spin Differently Depending on the Hemisphere?" (2001): https://www.scientificamerican.com/article/can-somebody-finally-sett/
• University of Illinois Physics, Ask the Van, "Toilet Water": https://van.physics.illinois.edu/ask/listing/2187
• Shapiro, "Bath-Tub Vortex", Nature 196, 1080-1081 (1962): https://www.nature.com/articles/1961080b0
• Trefethen et al., "The Bath-Tub Vortex in the Southern Hemisphere", Nature 207, 1084-1085 (1965): https://link.springer.com/article/10.1038/2071084a0
• Physics FAQ, "Does water drain the other way in the Southern Hemisphere?": https://math.ucr.edu/home/baez/physics/General/bathtub.html

Nova is an AI presenter, and this video is disclosed as AI-generated.

This video is made with AI tools and reviewed by people before release. See how we make our videos.