You may be dealing with a plumbing issue. You may get sent back in time and realize you don't have the strength to go on without indoor plumbing. You may get asked this by a small child who, up until that moment, was the one person who believed you had the answer to everything. Trust me. Sooner or later, you are going to want to know this.

Why does the water rush out of the bowl of the toilet so fast when the lever is in the tank? Why does a slow rush of water fail to clear the bowl completely? Why do toilets always seem to block up on Friday night before a long weekend? We can answer two of those questions with physics. The last will just have to depend on, oh, let's say karma.

Toilets have three major components. The first is a bowl. We all know what that's for. The second is a tank. We can all see that. The last is behind the bowl, in that little tube from whose bourn - hopefully - no traveler returns. That part is a siphon. As simple machines go, siphons get less respect than wheels, levers, or inclined planes; but to be fair, not that many people know that siphons make flush toilets possible. If they did, siphons would be celebrated.

A siphon works because it allows water to move like a chain instead of like discrete particles. Grab a pitcher and fill it with water. Stick a length of flexible tube deep in the water and let the tube droop down over the side of the pitcher. Then suck one the end of the tube until the water comes up over the edge of the pitcher and down the tube a ways. The water in the tube will splash on the floor. (Oops. Did I not tell you to put a container there to catch the water? My bad.) But the water in the length of tube climbing up the side of the pitcher will not fall back down into the pitcher. It'll keep going, drawing more and more water over the side until the pitcher empties onto the floor. (Really my bad. I mean. Did I have to tell you a whole pitcher? Couldn't I have just said a glass?) The water will be drawn over the side the same way a length of beads will be drawn over the side of a container if the beginning of the strand is pulled over the side.