The direction of the vortex "dahn the plug'ole" is due almost entirely to the physical shape and setting of the outlet in the basin and the piping immediately below it.

Tornadoes rotate counter clockwise in the northern hemisphere and I did read once, that they are exacerbated by cars driving on the right hand side of the road. It seems that the theory is, that two cars passing created a counterclockwise couple in the air. And much like the theory that loud noises can provide enough energy to trigger avalanches, they concluded that these small whirlwinds could create dust devils which could build up into tornadoes. They backed up the theory with graphs comparing the increase in tornadoes with the increase in motor traffic.

Bert.