Septic Tanks – What Are They?

Need to learn more about what exactly a Septic Tank is? the different types that are made and which will best suit your needs? Read our latest post for more information!

A septic tank is a large tank designed to take the wastewater from a home or business. They can be made from a variety of materials, including fibreglass, concrete, or brick. Although septic tanks are no longer used where there is a sewage treatment plant available, they are still a mainstay of rural homes and businesses. In particular, you can find them on older properties or on those that might not be suitable for a sewage treatment plant. They are also used for temporary measures, such as during a building project. About a third of homes in the US have a septic treatment system, but they're less common in the UK.

Septic Tank Design

Septic tanks are buried in the ground, allowing for inspection ports at the top, or are held above ground. The wastewater enters at one side and leaves through another pipe into the drain field or leach field. A septic tank is designed to separate the waste that comes from a property. As the waste moves through the tank, the heavier material sinks to the bottom and leaves the water on top. In a traditional septic tank, there are two main sections.

The first is the primary settlement tank, where the waste enters the tank from the property. Material that floats rises to the top of the tank, where bacteria colonises it so that it doesn't become too septic. Heavier material then sinks to the bottom. These layers are called the scum and sludge layers, respectively. That leaves a clearer "effluent" layer in the middle. The effluent moves into the second part of the tank, the secondary settlement tank so the same process can occur again.

In a modern fibreglass tank, the design is slightly different. They often have an inlet chamber, middle chamber and outlet chamber. However, the way that the different materials are separated works using largely the same process. Septic tanks are usually powered by gravity, so there's no need to hook them up to any power sources.

Types of Septic Tank

Septic tanks can be made using a few different materials and varying designs. They can be made from brick, concrete or more modern materials like fibreglass. Septic tanks come in different sizes too, with some suitable for up to 20 people. The most common type of septic tank in the UK is the "onion" shape, and there are also cylindrical tanks that are a popular choice too.

Brick and Concrete Septic Tanks

In the past, septic tanks were made from brick, stone or concrete. They featured the two-tank design, with the two tanks next to each other. Sometimes there would be three chambers. A pipe would often supply air to the tank too. You can still find these in some places, but this type of septic tank generally isn't installed anymore.

Onion-shape and Torpedo Tanks

The onion-shaped fibreglass septic tank commonly known as an Alpha Tank is now most commonly used in the UK. There's also the "torpedo" style tank, which is cylindrical and is known as an Low Profile Sigma Tank. Both of these types of septic tank go in the ground, like a traditional brick tank.

Above Ground Septic Tanks

There are also septic tanks that go above the ground, which are usually intended to be temporary. Unlike other septic tanks, they don't require planning permission. They are easily installed, with a range of sizes, and made from UV-protected polymers.

Inlets and Outlets

A septic tank has inlet and outlet pipes, where the wastewater enters and leaves. The inlet pipe ensures that the wastewater coming in is under the existing water line, slowing down the water, so there isn't too much disturbance. The outlet pipe is also under the water line so that it only takes the effluent layer out.

Access Points and Venting

As most septic tanks and installed below ground, they need access points so they can be monitored and maintained. A septic tank should also have a vent pipe to ensure that dangerous gasses don't make their way back into the property. Other systems of ventilation and prevention are used in the property to prevent the problem.


The soakaway is where the water goes to when it exits the septic tank. There are strict requirements concerning how the drain field is installed to ensure that the soakaway is colonised by anaerobic bacteria. The effluent runs through the soakaway to be filtered.

A septic tank can be a good waste disposal option if there is space and the soil is suitable. However, it's important to install one correctly, which is why you should understand how they work.

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