Secrets of the toilet

Way back on New Year's Eve of 2005, when we were still hosted over at Blogger, I did one of my more popular posts about how a toilet works. Most people don't know. I'm guessing they have some kind of vague mental image that when you push the toilet handle a trapdoor opens up somewhere and the contents of the toilet bowl fall through to the abyss. But that's not what happens and I felt compelled to explain it. The pretext was a long article from the Wall Street Journal about how toilets are tested. The official testing material is . . . miso (a Japanese fermented soybean paste). I thought of this again when I saw (hat tip boingboing) a video of a toilet that swallows just about anything (reasonable) you could put down it, including four full sets of chess pieces, three and a half pounds of dog food, bunches of hotdogs and much more. The video is at the end. To get to it you'll have to swim through my pool of past post on how a toilet works:

Most household toilets work using a bowl siphon. Yes, a siphon, just like you will be doing during the next gas crisis when you steal gas from your neighbor's car. You remember how you did that the last time, right? You put a tube into the gas tank and sucked some gas into it until the gas "went over the top of the bend" and, assuming the other end of the tube outside the car was lower than the level of the end in the gas tank, the siphon would empty out the gas in your neighbor's car into your gas can and you were on the road again (and also assuming you didn't suck the gas all the way into your mouth and wind up aspirating it and get an ensuing hydrocarbon pneumonitis).

So now we have three questions: (1) What makes a siphon work, anyway? (2) What does that have to do with flushing a toilet? (3) What does this have to do with miso?

(1) A siphon works by exploiting the difference in the weight of the water in the two columns. Here's a good way to visualize it. Suppose you have a length of chain, with an excess in a beaker and the rest running smoothly up over a pulley and back down to the table top. Now take the beaker in your hand and raise it. You'll find that the chain "runs out" of the beaker, over the pulley and down to the table on the other side. That's because the length of chain on the other side of the pulley is longer when you raise the beaker on the near side up, and the longer chain is heavier and pulls chain from the "lighter" (higher) side. Here is a good set of pictures of the set up.

(2) So where is the siphon in a toilet?

You can see from this picture there is a siphon in back of the bowl. When you push the toilet handle down, water from the tank in back of the toilet (not shown in this picture) starts to fill the toilet bowl more quickly than the water can flow over the siphon bend, and water, seeking its own level both in the siphon tube and the bowl, completes the siphon and the bowl empties. In fact it empties more quickly than the water runs into it from the tank, which is sized just right so that it refills the bowl again after it empties. The amount of water running into the bowl is sized so that when it is finished running the level is below that needed to complete the siphon. The valve from the tank now closes and water from your plumbing connection refills the tank and you are ready to "go" again. This explains how you can flush a toilet just by filling it from a bucket of water instead of the tank (you didn't know that? try it at home). There's a nice animation here.

(3) Back to miso.

For decades, the toilet industry had a standard way of testing a toilet's flushing capabilities: tossing 3/4-inch plastic balls into the bowl and pulling the handle. But there was one problem: Toilets that are fantastic at flushing down 3/4-inch plastic balls sometimes falter under real-world conditions.

A few years ago, researchers began pondering a better test. After scouring grocery aisles for alternatives, they settled on using miso, which is made primarily of cooked soybeans.

Now, a group of water utilities and plumbing companies is pushing to make the miso test the new standard. This month, the group, which includes Kohler Co. and American Standard Cos., is rolling out a set of rules called UNAR -- that is Uniform North American Requirements for toilet fixtures -- which lay out a flushing standard that toilets have to meet. A key element of the suggested rules, which also include standards for toilet parts, is the use of a miso paste in testing.

[snip]

Since 1978, toilet makers had been using the plastic-ball test, which involved dropping 100 balls into the toilet; the toilet had to dispose of at least 75 in one flush to pass. (Cheryl Lu-Lien Tam, The Wall Street Journal)

The article is long, and for some, "too much information," so suffice it to say the test involves fashioning miso paste into a cylinder to test flushing efficiency. The UNAR standard is meant to be like the "Energy Compliant STAR standard" for electrical appliances. In the 1950s we used 5 - 7 gallons to flush a toilet (toilet flushing is the largest use of water in the home--by far). That was lowered to 3.5 gallons subsequently, and in 1992 the Energy Policy Act required all new toilets to use only 1.6 gallons per flush. This ushered in the era of the skidmark and the dreaded double-flush. Now, with better designs, low volume toilets are finally getting it together. But manufacturers, and likely regulators, will want a good test for flushing efficiency. UNAR's miso test stands (floats?) poised to become that standard.

One more thing. Miso is the efficiency tester that "dares not speak its name":

Most manufacturers are careful to call the substance "soybean media" at the request of the miso merchants who sell the product. (The miso companies also insist that toilet makers not mention their names in connection with their testing.)

I guess they don't want to be identified with siphons, used to steal other people's gasoline.

And now the Olympic Champion of toilet flushing. Enjoy: