Indeed, things such as hurricanes and other large cyclonic systems are very much affected by the Coriolis Effect in terms of which way they spin. A hurricane might literally be 500 miles in diameter and last for many days; your sink or toilet is very small in comparison and the time the Coriolis Effect has to influence the draining water is very small as well.
In fact, when we are talking draining sinks, toilets, and bathtubs, the size and time scale are so small that the force is practically non-existent in terms of affecting the water in any way, especially when compared to the other forces in play; like the shape of the sink, the way the jets are pointed in the toilet, and things of this nature.
Plumbing Pro Tip of the Week
Tip #1 The twisting effect of the Coriolis force is real and does influence certain large things like the movement of air masses.
Tip #2 The effect plays no role in determining the direction in which water rotates as it exits from a draining sink or toilet.
Tip #3 Toilets and sinks drain in the directions they do because of the way water is directed into them or pulled from them.
Tip #4 If water enters in a swirling motion (as it does when a toilet is flushed), the water will exit in that same swirling pattern.
Tip #5 Most sink basins have irregular surfaces and are not perfectly level, a factor that can influence the direction in which water spirals down their drains.
TRIVIA ABOUT WATER: The Continental Divide in the Americas is the line that divides the flow of water between the Pacific Ocean and Atlantic Ocean. Rain or snow that drains on the east side of the Continental Divide flows toward the Atlantic Ocean while precipitation on the west side drains and flows toward the Pacific Ocean. (However, some rivers empty into the desert and don’t end up in the oceans.)
The continental divide runs from northwestern Canada along the crest of the Rocky Mountains to New Mexico. Then, it follows the crest of Mexico’s Sierra Madre Occidental. In South America, the Continental Divide lies along the Andes. Every continent except for Antarctica has a continental divide.
