Vortex Effect Tornado Making Tube

Simple, yet clever 1" dia. by 3" long plastic device to demonstrate the vortex effect of a tornado. Partially fill with water one of the two half-gallon size plastic soda bottles which you supply. Screw the bottles into opposite ends of the tube which we supply. Tip so the full bottle is on top and give it a circular starting whirl. Presto! You have a vortex. Call it a tornado if you're a meteorologist, a Charybdis if you're a classicist, or a whirlpool if you're into oceanography. Lots of fun and a fine opportunity to attempt to explain the effects of the earth's rotation on water draining out of a bathtub. The phenomena are related we're told, but good luck!!