Concerning drainage - A very simple visual lesson I offer students is to take a new synthetic sponge (flat, rectangular, color choice optional) and saturate it with water. Put it on a rack over a tray, long dimension horizontal, while I continue to talk. When the sponge stops dripping, stand it up on end (a la the 2001 monolith.) Never fails to astonish students how much additional water drips out the second time around. Can then squeeze the sponge to remove even more water. Add more precision to the exercise by A) measuring water needed to saturate sponge, B) measure how much drips from horizontal sponge, how much drips from vertical sponge, how much can be squeezed out. Judy in very windy New Jersey