You’ve likely heard that the directionality of the water swirl in a toilet flush is due to the Coriolis effect. It rotates counter-clockwise in the northern hemisphere and clockwise in the southern. However, that’s not exactly accurate. While the Coriolis effect does happen, it’s not significant enough to influence a toilet swirl.
Smarter Every Day and Veritasium have teamed up to explain just that, except they’ve done something marvellous this time. There are two videos, one on each of their channels that have to be played simultaneously for you to have the maximum viewing enjoyment. Yes, it’s the easiest thing to do, but I’ve made it a bit easier for you.