I share all this with you because I wanted you to know about the tank--I think it's a good investment that we can use throughout Schnickelfritz's education, but in the end I couldn't get the experiment to work when I tried it before class. The tubes need to be full of water when they're submersed in the tanks. I could hold my thumb over one end while I inserted the other, but because I couldn't fit my hand in the tank for the second end I had to move my thumb and the water immediately drained out. In hindsight, perhaps I should have used the expansion kit for the middle tank so I could remove my thunb under the water.
Instead, we did an experiment that's one the Science of Disney Imagineering DVD. Asa uses a glass jar filled with water and covers it with a Chinet plate before inverting it. The water stays in the glass even though it's upside down. My last minute search for supplies yielded plastic cups and plates. Here's what we learned--the plastic plates had a little give to them so if we filled the cups to the brim the weight (as the video suggests) the weight of the water would distend the plate and the water could escape. We were able to acheive the effect if we filled the cups 1/4 to 1/2 full, but it still took some care when inverting. You also needed to be careful holding the cup because if you squeezed it the pressure would force the water out. If it hadn't been a last minute substitution, I would have purchased rigid cups and plates. See the importance of trying experiments before doing them with the kids?