The Coriolis effect impacts the way water tends to circle before going down the drain. Many (most, all?) toilets are designed to work with the Coriolis effect. I am considering a line of toilets that would flush opposite of this, this is strictly a marketing device. But I am concerned that if the toilet design, forces the water to circle opposite of the Coriolis effect before going down the drain it could cause issues.

Is it problematic if we build toilets that flushes backwards?

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    $\begingroup$ I have trouble believing that you actually thought that the Coriolis Effect has any bearing on drains of any sort. And as a marketing tactic, it would backfire on you, since your potential customers would be laughing at you. We're trying to advance this SE site through its public beta phase, and frivolous questions like this undermine this effort. $\endgroup$
    – Dave Tweed
    Commented Feb 7, 2015 at 14:46
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    $\begingroup$ This question is based on false premise. $\endgroup$
    – SF.
    Commented Feb 7, 2015 at 19:19
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    $\begingroup$ In addition to what @SF. said, there's this Skeptics post. $\endgroup$
    – HDE 226868
    Commented Feb 7, 2015 at 20:04
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    $\begingroup$ I'm voting to close this question as off-topic because the question itself is based on a false premise. $\endgroup$ Commented Feb 9, 2015 at 17:15

2 Answers 2


Per the Wikipedia article on the Coriolis effect:

Contrary to popular misconception, water rotation in home bathrooms under normal circumstances is not related to the Coriolis effect or to the rotation of the earth, and no consistent difference in rotation direction between toilet drainage in the Northern and Southern Hemispheres can be observed.

Only if the water is so still that the effective rotation rate of the earth is faster than that of the water relative to its container, and if externally applied torques (such as might be caused by flow over an uneven bottom surface) are small enough, the Coriolis effect may determine the direction of the vortex.

You can be forgiven for believing this to be true though. Again from the Wikipedia article:

The idea that toilets and bathtubs drain differently in the Northern and Southern Hemispheres has been popularized by several television programs and films, including Escape Plan, Wedding Crashers, The Simpsons episode "Bart vs. Australia", and The X-Files episode "Die Hand Die Verletzt".[30] Several science broadcasts and publications, including at least one college-level physics textbook, have also stated this.[31][32]

  • $\begingroup$ I suspect that " ... the effective rotation rate of the earth is faster than that of the water relative to its container, ..." is trying to compare in-container velocity with the DIFFERENTIAL velocity due to global rotation along the Nth-Sth axis of a vessel. | A REALLY ROUGH calculation suggests a differential velocity of about 0.5 mm/s per metre of pool diameter. For a toilet of say 200mm (if that) dia the difference is around 0.1 mm/s. That's vv easily swamped. | For a 10m pool you get about 5mm/s differential velocity at nth & sth ends of N-S axis - a demo MAY be doable. Or not :-) $\endgroup$ Commented Feb 11, 2015 at 12:19

Per the ever informative Snopes The hemisphere doesn't affect the spin of the water. This means that the water spin down the drain is controlled by the design of the drain. This shouldn't be hard to design for.

  • $\begingroup$ eyrie.org/~dvandom/Edu/newcor.html confirms this. At the end of Sect. 5.2 it states if you don't see the Coriolis in water draining out of sink " ... don't blame it on the Coriolis effect unless your sink is the size of a small ocean" $\endgroup$
    – Fred
    Commented Feb 7, 2015 at 12:58
  • $\begingroup$ See my comment on Chris's answer - a 10 metre diameter tank MAY be able to demonstrate the effect with due care. | As a child (young teenager?) I tried many times to consistently achieve the claimed effect with a bathtub and was disappointed at not being able to do so. $\endgroup$ Commented Feb 11, 2015 at 12:21

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