There is no denying that the toilet is one of the most important compartments in any household, business place, or any place where people are occupying. But the truth is, even though we can’t imagine life without a toilet, it is the last thing we ever want to think about. For good reasons, we associate the toilet with human waste, stench, nasty germs, which create negative mental images. While all this is true, we are here to tell you that a toilet takes brilliant engineering to make life easier and sanitary for all of us. We will be uncovering the engineering involved to make the toilet function the way it does. First, most toilets consist of two main compartments:

The tank– is the top part that is normally placed against the wall and stores water. It contains the following components: fill valve, flush valve, overflow tube, and flapper.

The bowl- it drains out into the siphon, and some hold the toilet seat while others require one to squat over depending on the specific toilet model.

The toilet has three mechanisms that are interrelated in their functionality:

  • The bowl siphon
  • The flush mechanism
  • The refill mechanism

Next, we will look at each of these mechanisms.

The Bowl Siphon

Did you know that even if you disconnected the tank and left the bowl, you would still flush? The bowl is what causes the flush and is perhaps the most important part of the toilet. Molded into the bowl, is a crucial mechanism, called the bowl siphon. As shown below.

The function of the siphon is to suck water out of the bowl and down the sewer pipe. To understand better, you do the following with your toilet.

Pour a cup of water into the bowl and observe what happens. You will find nothing happens. Pour some more cups one at a time and observe. You will notice that nothing happens- the toilet bowl’s water level remains the same. This is because, as you can see in our diagram above, when you pour a cup of water in the bowl, the water rises, but the extra water spills over the edge of the siphon tube and drains away in the sewer drain.

Next, pour a bucketful (2 gallons) of water into the bowl. You will notice that almost all the water will be sucked from the bowl and down the pipe, making a flush sound. This is because you have poured enough water into the bowl, fast enough to fill the siphon tube, resulting in all the water being sucked from the bowl and down the sewer pipe automatically. The other thing to notice is that as soon as the bowl empties, air enters the siphon tube producing a gurgling sound and stopping the siphoning process.

So as we said earlier, you can flush your toilet, even without the tank so long as you have a bucketful of water.

The Flush Mechanism

It consists of the tank and flush valve. The tank acts as a capacitor. It holds like 2 gallons (7.6 liters) of water, which takes about 30 to 60 seconds to fill up. Once you flush all the water in the tank rushes into the bowl in less than three seconds. (Just like pouring water from the bucket in one motion)

The tank has a handle on the side attached to a chain inside the tank. The chain is also linked to the flush valve. Once you pull on the tank handle, it pulls the chain, which lifts the flush valve. The flush valve moves out of the way, exposing a 2-3 inch wide drain hole, through which water flows into the bowl. In most toilet bowls designs, the water enters the rim, with some draining from the rim holes. The water flows down the bottom of the bowl into a larger hole, known as the siphon jet. The siphon jet releases most of the water directly into the siphon tube, causing the water and waste in the bowl to be sucked out.

The refill mechanism

The purpose of the mechanism is to fill the tank again with enough water to start the next flush. The refill mechanism starts when the water level in the bowl and tank drops. It uses a valve to turn the water on and off. The valve turns the water on when the ball float (filler float) falls to the bottom of the tank covering the drain hole to allow water to fill the tank. When this happens, the filler valve (or refill valve) sends water in two directions: down the refill tube into the tank and the overflow tube into the bowl.

As the water level in the tank rises, the ball float also rises. Once the water reaches the predetermined level, the float will have risen far enough to turn the valve off. Any extra water will be drained by the overflow tube into the bowl to prevent the tank from overflowing, causing flooding. This can happen if the filler valve became faulty or the float was detached.

A recap of the toilet mechanism

  • Pulling on the handle on the tank tags 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 assumes its position.
  • This rush of water activates the siphon in the bowl. The siphon sucks everything in the bowl down the drain.
  • Meanwhile, as the level of the water in the tank falls, so does the floating. The falling float turns on the refill valve.
  • Water flowing through the refill valve refills both the tank and the bowl. As the tank refills, the float rises until it reaches the preset level, and the refill valve shuts off.
  • In case something goes wrong or the refill valve keeps running, the overflow tube will prevent flooding by directing the excess water into the bowl.
  • The waste water goes into the sewer or septic tank.

How Toilet Works Diagram

How Toilet Works In Airplane

We have already seen that most toilets use the siphon or gravity to empty the bowl’s content into the sewer line. However, in an airplane, the motion or turbulence would cause the water in the bowl to splash out.

Instead of using passive siphon, airplane toilets use an active vacuum, hence being called vacuum toilets.

When you flush, a valve is opened in the sewer line. The vacuum in the line sucks the contents of the bowl and into a tank. As a result, these toilets use just a little water (or the blue sanitizing liquid used in airplanes) to clean the bowl. Most vacuum toilets flush with only half a gallon (2 liters) of fluid or less, compared to 1.6 gallons (6 liters) for a water-saving toilet and up to 5 gallons (19 liters) for old toilets.

How Toilet Works In RV

A recreational vehicle, often abbreviated as RV, is a motor vehicle or trailer that includes living quarters designed for accommodation. 

As we have seen, fixed toilets have a back-mounted tank that fills and flushes the bowl through water pressure. In the case of RV toilets, water is supplied from the fresh water tank and usually refilled from an on-demand pump or city water source.

In most standard RV toilets today, you may be required to put some water into the bowl before using it and then start the flushing mechanism from a foot pedal or handle that opens the flushing door from the bowl to the pipes. Newer coaches have electric flushing systems that create water pressure to help rinse the bowl out.

Even though your RV toilet may have some water to rinse the bowl and fill its bottom, water pressure is too low to push waste out of the bowl. Instead, the toilet uses gravity to push waste from the bowl through 3 inches-thick pipes into the RV’s black water tank. The tank collects all of the waste until it is emptied through a flexible hose into a septic system. The advantage of this system is that only a small amount of water is used to conserve your fresh water tank.

How Bio Toilet Works

Bio toilet is a type of toilet system which disintegrates and decomposes human waste into water and biogas. Unlike standard toilets, the Bio-toilet has a Bio-digestion tank where the decomposition takes place. The decomposition is done by specific high-grade anaerobic bacteria that convert the waste into methane gas, carbon dioxide gas, and water.

Bio-toilets consist of two compartments: the toilet and Bio-digestion toilet tank. The toilet may be a water closet or a squatting pan, with the drain connected to the Bio-digestion tank.

The Bio-digestion tank has several chambers to process human waste in different stages. It also has three output valves. One removes the foul smell, the other one removes gases like methane and carbon dioxide, and the additional one water.

Once the human waste is flushed from the toilet, it goes into the bio-digestion tank. The toilet has the water trap system, which prevents air from entering the tank. Also in the tank are four types of anaerobic bacteria for processing the waste. These high grade bacteria can withstand a wide range of temperatures from freezing temperatures (-5 degree Celsius) to 80 degrees Celsius. This ensures they are unaffected even by cleaning detergents used to clean the toilets. 

The bacteria decompose the waste into methane gas, carbon dioxide, and water. The Methane gas is sent through the vent and can be stored for use in the kitchen for cooking or used in the methane generator to produce electricity. The water, on the other hand, can be treated for recycling.

Bio-toilets are environment-friendly, reduce sewage problems, and conserve water. While the most water-saving standard toilet uses 3-6 liters of water for flushing, Bio-toilets use only 0.5 to 1 liter. Also, they are a source of energy (methane for cooking).

How Bio Toilet Works In Train

Trains especially in India, use bio-toilets to keep the undercarriage and tracks clean and free of human waste deposits.

The bio-toilet consists of a holding hank that is fitted under the rail coaches underneath the lavatories. This holding tank is made up of stainless steel and consists of 6 compartments. A toilet pan is directly connected to the holding tank using a pipe to carry the human waste into the tank. Once inside the tank, the waste is decomposed by the special anaerobic bacteria into methane, carbon dioxide, and water. The gasses are released into the atmosphere while the water is chlorinated before being discharged. Below is a flow diagram to demonstrate how the waste is decomposed:

How does toilet bowl works

As we have said earlier, the toilet bowl carries out the flushing mechanism using the in-built siphon.

For the mechanism to occur, you need to pour enough water (like 2 gallons) into the bowl in one motion (fast). This can be done from the toilet cistern or tank when you pull the handle or from a bucket. This rushing water fills the siphon tube, causing the siphon to suck all the water from the bowl. Meanwhile, the siphon tube fills with air, making the familiar flushing sound.

How Do Toilets Work?

When a toilet is flushed, the following happens:

  • The handle pulls a chain, which in turn raises the flapper and releases the tank water into the bowl.
  • The water is drained out into the bowl siphon.
  • Once the tank is empty, the flapper closes, and the fill valve is activated to start refilling the tank.
  • The tank fills with new water, which travels up through the base of the valve, through the refill tube, and then back down through the overflow tube.

How a toilet cistern works

A cistern is simply the tank component of a toilet. Its purpose is to store and release water into the bowl within seconds of the handle being pulled. This process is basically mechanical, and water flows down into the bowl through the force of gravity, rinsing the bowl and taking along all the nasty stuff into the sewer pipes.

When you lift the lid on the cistern on a toilet, you will find a chain, flushing valve, and a floating ball. The water in the cistern drains when the valve is removed from its resting position at the bottom. The balloon-like object (floating ball) rises and drops in tandem with the water level. When it falls, it tilts the white plastic lever, opening a ball valve (also called a ball cock) and allows the cistern to refill. As the water rises, the floating ball rises with it, tilting the lever and slowly shutting off the ball valve.

How Kohler toilet works

Kohler Co. is one of the most popular brand names when it comes to toilets and kitchen appliances. They have a wide range of modern toilet designs. Their toilets function by using the force of gravity and a change in pressure.

Kohler toilets consist of a tank that acts as a storage reservoir for water. It also has a fill valve and a flush valve which regulates the flow of water in the tank. The tank can be mounted or molded into the bowl as one unit depending on the specific Kohler toilet. The bowl has an outlet that leads to a large diameter curved pipe (trapway) at the rear, which carries waste material to the sewer pipes.

Normally, a small amount of water remains in the toilet bowl because the pressure inside the bowl and the pressure inside the trapway are equal. When the trip lever is depressed, it activates the flush cycle by opening the flush valve flapper, allowing water to pour from the tank to the bowl through the force of gravity.

The rush of water to the bowl quickly fills the trapway displacing the air space within the trapway. This results in pressure changes causing a siphon to be activated. Water and waste in the bowl are drawn out through the trapway and into the sewer line by the force of the siphon.

When the tank is emptied, the flush valve flapper closes, and water flow to the bowl stops. Air gradually reenters the trapway, the pressure equalizes, and the siphon stops.

When the water level in the tank starts dropping, a floating ball mounted on the fill valve begins to travel downwards, activating the fill valve and initiating the refilling of the tank and the bowl with fresh water. As the tank refills, the float also rises with the incoming water. The fill valve shuts off when the tank water height reaches the predetermined level. And the toilet system is ready for the next flush cycle.

How Japanese toilet works

Japanese toilets are currently the most sophisticated toilet around the world. One brand name in particular that stands out is the Toto toilets. Generally, these toilets have the same construction as the western toilets. They use porcelain, similar water tanks, piping and flushing mechanism and other fixtures. They also use water pressure and gravity to push the waste from the bowl into the sewer system.

These Hi tech Japanese toilets are called washlets. In addition to offering the ordinary toilet function, they feature innovations aimed at enhanced cleaning and superior comfort. They are electric powered and operated using a remote near or attached to the toilet seat or on the wall.

The basic feature (which is extra in comparison to standard western toilets) in all of these Japanese washlets, is the bidet. It is a nozzle the size of a pencil protrudes from underneath the toilet seat for squirting water. It has two settings: one for washing the bottom and one for the female genital area. The former is called posterior wash, family cleaning, or general use and the latter is known as feminine wash, feminine cleaning or simply bidet. The most impressive thing is that the nozzle is self-cleaning before and after use. Plus, it never touches the body of the user at any point. The user selects what area to clean by pressing the corresponding button on the control panel. Typically, the same nozzle is used for both operations, but it has differently positioned openings to squirt water at different angles aiming to hit the correct spot. The control logic is connected to a proximity sensor in the toilet seat, so it operates only when the seat is occupied.

Aside from the bidet, the Japanese washlets have other dazzling arrays of features like a blow dryer to dry the user up after cleaning, seat heating, massage options where the user selects either pulsating or vibrating water jet, water adjustments to the user’s preferred temperatures and pressure, automatic lid opening, automatic flushing, room heating and air conditioning for the room—included either as part of the toilet or in the seat, and some toilets can mix water jet with soap for thorough cleaning.

How Siphon Jet Toilet Works

Inside the toilet is a drain pipe called the siphon tube. The lower portion of the tube is curved to trap sewer gases and keep them from coming back up into the bathroom. It also creates a partial vacuum inside the rest of the tube, which is normally filled with air.

When you flush the toilet, water rushes from the tank into the toilet bowl. It enters the bowl via a larger opening, known as the siphon jet. The siphon jet releases most of the water directly into the siphon tube. This rapid influx of water raises the water level inside the siphon tube, changing the air pressure. The change in pressure causes the siphon to push both the water and waste up the tube and down the drain into the sewer line.

How mobile toilet works

Mobile toilets are also known as portable toilets. They are small units made of a lightweight molded plastic construction. Unlike standard toilets which are plumbed into the ground and connected to sewer lines or septic tanks, mobile toilets have no plumbing at all. They are self-contained toilets with a holding tank for collecting the waste and therefore require to be emptied frequently. The advantage of these movable toilets is that they can be stationed anywhere. It is the reason they are mostly used for hire when there are large gatherings for different events. They may also be used in recreational cars and on small boats. But they are ideal for short use durations.

As we have said, these toilets hold the waste in, and it keeps accumulating with use. Chemicals are added from the holding tank into the waste to counteract the odor and appearance of the waste. They also help in breaking down the waste. Modern toilets also use microbial and enzymatic agents which are very effective at reducing odor by accelerating digestion and breakdown of the waste.

These toilets need regular servicing to replenish toilet paper, water and cleaning and to retain hygiene standards. The chemicals and microbial agents used also require frequent replacement to maintain efficacy.

The toilets have the following main compartments:

  • Holding tank
  • Toilet seat
  • Flushing mechanism
  • Pressure system

Holding tank:

it stores all the waste from the toilet. It is usually located beneath the toilet seat or pan and is used to collect the waste from the toilet. It also contains chemicals used to break down the waste before emptying. Additionally, it gives the toilet stability since the structure of the toilet is light.

Toilet Seat:

A mobile toilets can have a seat or a pan that the user squats over.

Flushing mechanism

The flusher is operated either by handle or pedal. These toilets flush using either water from a hidden tank within the toilet or toilet chemicals from the holding tank. Once you flush, the pump flush system creates pressure which circulates the water and chemicals through a pipe to be transported to the toilet pan. The water or chemicals together with the waste in the toilet pan go to the holding tank, located beneath the toilet seat or pan. This tank holds all the waste and liquids. Inside the holding tank, chemicals break down the solid waste, kill germs, and remove foul smell.

The toilets are regularly serviced to replenish toilet paper, water and cleaning and to maintain hygiene standards.

Pressure system:

Pressure sytem is used to circulate water and chemicals from the holding tank and to the toilet pan.

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