Seems like there's plenty online to suggest it is a myth, for example from Wiki (which although I'm sure you'll point out can be edited by anyone)..
Quote:
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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.
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