[CORed]

I think most toilets are designed so that the water rotates in a particular direction. If you watch a sink or bathtub drain, however, you will see that the vortex can rotate in either direction, with the movement of water in the sink or tub before you pull the plug determining which direction. You can even force the direction to reverse by moving your hand through the water like an oar so that it generates a vortex, and causing that vortex to move over the drain.

Yes, I spent way too much time playing in the bathtub when I was a kid.