The toilet. The commode. The john. The loo. The
porcelain throne. No matter what you call it, it is
inevitable that we come to discuss this device, because every
home has at least one. But more important, we'll discuss the
toilet because it is a technological marvel -- a fascinating
But it has all of these bad connotations in our minds.
There are the things we do with a toilet, the germs we
associate with it, the images we have from public restrooms,
the fact that we have to clean it... all of these details
leave the toilet somewhat... tainted. In this edition of How Stuff
Works, I ask that you try to get past the mental block
and simply look at toilets for what they are -- neat solutions
to a problem -- because toilets really are amazing things!
Parts of a Toilet There are several
interrelated components that make a toilet do what it does, as
Note: The water level as it relates
to the siphon action is simplified in this animation. In
reality, the water level does not remain constant as the water
flows down the tube.
If you take off the tank cover and peer inside, you will
see all of these parts. They might look slightly different in
your particular toilet, but they are all there in one form or
another. The three main systems that work together are:
The bowl siphon
The flush mechanism
The refill mechanism
Let's look at each of these
parts separately until the secrets of the toilet are revealed.
The Bowl Siphon Let's say that you somehow
disconnected the tank, and all you had in your bathroom was
the bowl. You would still have a toilet. Even though it has no
moving parts, the bowl solves all of the problems a toilet
needs to solve. The crucial mechanism that is molded into the
bowl is called the bowl siphon, shown here:
to "Webster's New World College Dictionary (4th Ed.)"
porcelain is "a hard, white, nonporous, translucent
variety of ceramic ware." "Merriam-Webster's Collegiate
Dictionary" further defines porcelain as
"...[consisting] essentially of kaolin, quartz and
feldspar, and is fired at high temperatures."
In other words, porcelain is pottery made of a
special white form of clay. It is molded in a liquid
form, dried as greenware, painted with glaze and then
fired in a kiln. A toilet bowl is generally molded in
two halves which are attached together in the greenware
state. The tank and tank lid can be molded as one piece.
You can understand how the siphon works by trying two
experiments with your toilet. First, take a cup of water and
pour it into the bowl. You will find that approximately
nothing happens. What's even more interesting is that you can
pour 25 cups (6 L) of water into a toilet, one at a time, and
still, nothing will happen. That is, no matter how many cups
of water you pour in, the level of the water in the bowl never
rises! You can see in the figure why this is the case. When
you pour the cup of water in, the water level in the bowl
rises but the extra water immediately spills over the edge of
the siphon tube and drains away.
Now, take a bucket of water -- approximately 2 gallons (7.6
L) -- and pour it into the bowl. You will find that pouring in
this amount of water causes the bowl to flush. That is, almost
all of the water is sucked out of the bowl, and the bowl makes
the recognizable "flush" sound and all of the water goes down
the pipe. What's happened is this: You've poured enough water
into the bowl fast enough to fill the siphon tube. And once
the tube was filled, the rest was automatic. The siphon sucked
the water out of the bowl and down the sewer pipe. As soon as
the bowl emptied, air entered the siphon tube, producing that
distinctive gurgling sound and stopping the siphoning process.
You can see that, even if someone were to cut off the water
to your bathroom, you could still flush the toilet. All you
need is a bucket containing a couple of gallons of water.
The Flush Mechanism The purpose of the tank
is to act like the bucket of water described in the previous
section. You have to get enough water into the bowl fast
enough to activate the siphon. If you tried to do that using a
normal house water pipe, water would not come in fast enough
-- the siphon would never start. So the tank acts as a
capacitor. It holds several gallons of water, which it takes
perhaps 30 to 60 seconds to accumulate. When you flush, all of
the water in the tank is dumped into the bowl in about three
seconds -- the equivalent of pouring in a bucket of water.
There is a chain attached to the handle on the side of the
tank. When you push on the handle, it pulls the chain, which
is connected to the flush valve. The chain lifts the flush
valve, which then floats out of the way, revealing a 2- to
3-inch (5.08- to 7.62-cm) diameter drain hole. Uncovering this
hole allows the water to enter the bowl. In most toilets, the
bowl has been molded so that the water enters the rim, and
some of it drains out through holes in the rim. A good portion
of the water flows down to a larger hole at the bottom of the
bowl. This hole is known as the siphon jet. It releases
most of the water directly into the siphon tube. Because all
of the water in the bowl enters the tank in about three
seconds, it is enough to fill and activate the siphon effect,
and all of the water and waste in the bowl is sucked out.
The Refill Mechanism So the bowl will flush
as long as we dump enough water into it to activate the
siphon. And the purpose of the tank and the flush valve is to
hold and then dump about 2 gallons (7.6 L) of water very
quickly into the bowl. Once the tank has emptied, the flush
valve resituates itself in the bottom of the tank, covering
the drain hole so the tank can be refilled. It is the job of
the refill mechanism to fill the tank back up with enough
water to start the whole process again.
The refill mechanism has a valve that turns the water on
and off. The valve turns the water on when the filler
float (or ball float) falls. The float falls when the
water level in the tank drops. The filler valve (or
refill valve) sends water in two directions, as shown in this
Some of the water goes down the refill tube and starts
refilling the tank. The rest goes through the bowl refill
tube, and down the overflow tube into the bowl. This refills
the bowl slowly. As the water level in the tank rises, so does
the float. Eventually the float rises far enough to turn the
valve off. What would happen if the float were to become
detached, or the filler valve were to jam so that it never cut
off? Theoretically, the tank would overflow and flood the
bathroom. But the overflow tube is there to prevent that from
happening, directing the extra water into the bowl instead of
onto the floor.
Putting It All Together
that you have seen all the parts, you can understand the
Pushing on the handle pulls the chain, which releases
the flush valve.
About 2 gallons (7.6 L) of water rush from the tank into
the bowl in about three seconds. The flush valve then
This rush of water activates the siphon in the bowl. The
siphon sucks everything in the bowl down the drain.
Meanwhile, when the level of the water in the tank
falls, so does the float. The falling float turns on the
Water flowing through the refill valve refills the tank
as well as the bowl. As the tank refills, the float rises,
and when it reaches a certain level the refill valve shuts
Should something go wrong and cause the refill valve to
keep running, the overflow tube prevents a flood.