The way I read it was that it is caused by the earth spinning BUT Coriolis only applies to objects unattched to anything on the earth like a projectile or even a ball (if one could be thrown far enough), thhe effect is for the projectile to veer to the right in the N.hemisphere & vicky-verky in the S..
Gents, I must confess I had to Gogle it, and found that Stuart Little is quite correct. I stand corrected.
(I suppose in the case of the bathwater, the water IS "connected" to the earth - through the bath itself, the plughole, pipery, drains, etc, etc, so it's not coriolis effect). BTW, in my googling I found a very interesting short vid. A guy gives a football to 2 kids, then seats them opposite each other on a playground roundabout. While the roundabout doesn't rotate, the kids can throw the ball back and forwards to each other no problem, but when the guy turns the roundabout at a reasonable speed, the ball apparently veers off to the side, missing the opposite kid by "miles". One could of course argue that during it's flight the ball is not connected to the earth, but it does carry the rotation of the roundabout with it when it leaves the thrower's hands. A bit like the 1,010 mph fly trapped aboard Concorde - normally flies at "10 mph", but when aboard Concorde, add the 1,000 mph to that (unless he's flying toward the tail)!).
WHAT a fuss I've made in the Jokes thread. Sorry ....... hat, coat .....