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09-Feb-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? --T.J. Crapper, Chicago
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 ... I
figure 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 is not as severe
as it might seem at first thought. For one thing, flowing water tends to adhere to a
surface, such as the inside of a pipe, and the friction slows things down a good deal.
There's also a phenomenon known as "terminal velocity," which skydivers are
familiar with: after you fall through the air for a certain period, 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 whatnot.
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 was not 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 is one set of technical
terms that nobody above the age of 12 is going to misunderstand.
--CECIL ADAMS
The Straight Dope / Questions or
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