Firstly, wikipedia is not a legitimate source of information as it is all user maintained and thereby prone to error. (Not that their definition looks wrong or anything, I just don't give wikipedia any credit because of it's fallability.)
Secondly, from what they are saying, in order to make the water go in a reverse direction, you would basically need to set up a science experiment, which wasn't what we were being asked. If you go flush any random toilet or fill any random sink in the northern hemisphere, it'll drain the same way.