Do Toilets Really Flush Backwards in Australia?

Do toilets really flush backwards in Australia? No. The Coriolis effect is real, but in a toilet bowl it is far too weak to matter: the angled jets under the rim decide which way the water swirls, in either hemisphere.

The Simpsons spread the idea in "Bart vs. Australia" (Fox, 19 February 1995), where Bart phones Australia to check which way a drain spins. The effect the show blamed does exist: it sets the spin of hurricanes. At bowl scale it loses to the jets, the bowl's shape and the leftover currents from filling. The one time it was caught in a drain took a bathtub-sized tank, left still for a day and drained slowly: counterclockwise at MIT in 1962 (Ascher Shapiro, Nature) and clockwise at the University of Sydney in 1965 (Trefethen and colleagues, Nature). In 2015 Veritasium and Smarter Every Day repeated it with pools in Sydney and Alabama. So it is true, if your toilet is a bathtub and you wait a day to flush.

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