How to Flush a Toilet

Yesterday I was over at a friend's house for a vegetarian potluck, and in case that doesn't give it away, these folks are hardcore about their environmental stewardship, and so I thought I might share something of things I learned that night.

Until yesterday I had never really wrapped my head around what makes a toilet flush. I knew the tank fills with water until you push the lever, which opens a valve which lets water rush into the bowl... and then... yea... it all goes away... magically :)

So I was shocked to hear that they save their kitchen dishwater in a bucket and then use that to flush their toilets just by dumping it in. What? How does that work?

"Well, my hippie friend explained you see the shape of that pipe? ** if you're unfamiliar with the shape you should really get up right now and go look under your kitchen sink and notice the "S"-shaped curve** Once you fill it up to the top of that curve but there's still more water rushing in, it pushes it over the top of the curve and back down, and that creates a syphon, which sucks the rest of the water and whatever else down the pipe."

"So if you go slowly the water level gets to the top of the curve and then it just trickles over the top of the curve, so it's got to have some amount of speed to it." (Another one of the guys right there said, "Have you ever taken a pee so big it flushed itself?"
:P )

I still didn't believe him, so he was like "come try it! Only the light for the upstairs bathroom is broken so we'll have to take this candle." I hope you can imagine three hippies groping the walls of the creaky upstairs trying to get to the bathroom by this little candle, and then all of us sitting on the floor in the bathroom. While Erok held the candle somewhat over the toilet I got to pour the bucket of water, which had recently been in the tub. They save their tub water for this purpose as well, and also to let the heat radiate out into the room.

Syphons, suction, and fluids are not my forte, but that just makes them all the more amazing to me. I still have a deep sense of awe for fluid dynamics.