Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
The Coriolis effect does not determine the direction that water rotates in a bathtub drain or a flushing toilet. The Coriolis effect induced by the Earth's rotation becomes significant and noticeable only at large scales, such as in weather systems or oceanic currents. In addition, most toilets inject water into the bowl at an angle, causing a spin too fast to be significantly affected by the Coriolis effect.