I fully agree that you can't trust toilets because it is induced by the direction the jets come out of the bowl.
I ran very careful experiments and made sure that the water in the two sinks and bathtub I tried it in contained completely stagnant water.
I even tried to induce a pre rotation in both directions. It didn't matter.
Counter Clock wise in the Southern hemisphere.
Before coming down here I was convinced it was a myth.
Now I really want to find out for sure.
So what direction does your Northern hemisphere drain rotate
Googled it and this was the best explanation I found.
So maybe I am wrong on the Southern hemisphere direction.
“All this was demonstrated way back in 1962 by one Ascher Shapiro, a
researcher at the Massachusetts Institute of Technology. Shapiro
filled a circular tank six feet in diameter and six inches high in
such a way that the water swirled in a clockwise direction. (Remember,
now, that Coriolis forces in the Northern Hemisphere act in a
“Shapiro then covered the tank with a plastic sheet, kept the
temperature constant, and sat down to read comic books or whatever
scientists do while they wait for their experiments to percolate. When
he pulled the plug after an hour or two, the water went down the drain
clockwise, presumably because it still retained some clockwise motion
“On the other hand, if Shapiro pulled the plug after waiting a full 24
hours, the draining water spiraled counterclockwise, indicating that
the motion from filling had subsided enough for the Coriolis effect to
take over. When the plug was pulled after four to five hours, the
water started draining clockwise, then gradually slowed down and
finally started swirling in the opposite direction.”