Wanderlust World Wanderlust World The Coriolis effect influences large-scale fluid motion (weather systems, ocean currents) but is negligible in sinks/toilets. In everyday drains, the swirl direction is determined by basin shape, initial water motion, and plumbing—not hemisphere.
Myth buster: The idea that sinks drain opposite ways in the Northern vs. Southern Hemisphere is a popular misconception; the effect is too weak at that scale.