A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

When a toilet atop the Sears Tower is flushed, do the contents fall 110 floors?

February 9, 1979

Dear Cecil:

Something has puzzled me for years. Suppose I worked on the 110th floor of the Sears Tower. Nature has reminded me it's time to relieve myself of last evening's supper. Now, I can't imagine the pileup of poop that would splatter all over the Wacker Drive sewer system if the stuff went straight down the tube. Do they have some kind of diversionary piping system, or does it indeed drop 1,450 feet to street level?

Cecil replies:

When you look at modern architecture, T., you're supposed to think about the glories of civilization, not toilets. Although now that you mention it, one does wonder about the plumbing arrangements. Well, wonder no more. Having made my usual discreet inquiries … you definitely want to avoid saying things like "splatter" … I can tell you the answer is no, the stuff doesn't drop in a straight shot from the top floors. There are offsets in the soil pipes every so often where the water runs horizontally for a short distance and then down again. Some of these were included just as a matter of convenience — the pipes were in the way of something else — and others were put in for the express purpose of slowing down the water.

The problem with water running downhill and picking up a lot of momentum isn't as severe as it might seem. For one thing, flowing water tends to adhere to a surface, such as the inside of a pipe, and the friction slows things down considerably. There's also the phenomenon known as "terminal velocity," which skydivers are familiar with: after you fall through the air awhile, you reach a maximum speed. For water inside a pipe, this usually comes out to around 10 to 20 feet per second, depending on the diameter of the pipe and such.

The more serious difficulty in a drain system of any kind (not just Sears's) is venting. Bathroom waste releases a lot of gases, which have to escape somewhere. Additionally, when you have a large volume of water falling down a stack, the air beneath has to get out of the way without creating a lot of turbulence — the glug effect, to put it in technical terms. To alleviate both problems, vent pipes are cut into the soil stacks at regular intervals to help relieve the pressure.

Waste water runs into a catch basin below street level and thence into the city sewer system. Toilets on the basement levels drain into a sump at the very bottom of the building, the contents of which are pumped up to sewer level from time to time.

The real challenge in Sears Tower wasn't so much getting the water down — after all, gravity does most of the work — as getting it up there in the first place. Street pressure is only good for the first four or five floors in an ordinary building. Sears has a series of pumps and tanks located in the basement, the 31st floor, the 64th floor, and the 88th floor. Water is pumped up under high pressure from one tank to the next, and then drains to the faucets in bathrooms and other facilities below. A few fixtures operate directly off the high-pressure line by means of pressure-relief valves.

Plumbing is a fascinating topic, no doubt about it. As a child, for example, I was scandalized to learn that plumbing catalogs routinely described pipe fittings as "male" and "female." But then I thought: here's one set of technical terms nobody above age 12 is going to misunderstand.

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A Straight Dope Classic by Cecil Adams
A Straight Dope Classic by Cecil Adams
A Straight Dope Classic by Cecil Adams
A Straight Dope Classic by Cecil Adams
A Straight Dope Classic by Cecil Adams
A Straight Dope Classic by Cecil Adams
A Straight Dope Classic by Cecil Adams
A Straight Dope Classic by Cecil Adams
A Straight Dope Classic by Cecil Adams
A Straight Dope Classic by Cecil Adams
A Straight Dope Classic by Cecil Adams

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