What's an easy and good experiment with Hydrostatic paradox?

This is a real eye bender. Look at Figure 4 here. If that doesn't knock your socks off, nothing will.

http://scubageek.com/articles/wwwparad.html

The only question is how do you build it? I think a metal retainer mounnted on the bottom and on both sides of a box would work. You could calk the membrane to make sure it is water proof. Not funny but astonishing if you are looking at the hydrostatic paradox.

I think you would do well just to make something that is an example of a hydrostatic paradox.

You could start with stiff pvc tubing (home depot). Drill a hole for 3 different bottle caps of pop bottles. Drill different size holes in the caps. Not too big. Glue the caps into the tubing. Use three different sizes of pop. (2 liter 1 liter 500 mL). Seal the ends of the pvc tubing with the glue meant for doing this. Cut the bottom off the pop bottles.

When the glue is dry on caps and ends, put the bottles in their caps. fill with water. The paradox should be illustrated. This shouldn't cost an awful lot to do. Actually you could glue the the bottles themselves into the pvc tubing a calk the joint after gluing.