Septic Tank & Cesspits – What is The Difference?

Septic Tank & Cesspits – What is The Difference?
28/05/2021 Joshua George

Whilst discussing the removal of sewage and wastewater might not be the sexiest subject, it is integral to the smooth running of any home or business.

Why Would I Need A Septic Tank or Cesspit?

In the UK, there are precise building regulations relating to sewers. They clearly state that wherever possible, every property must be connected to the mains system. This enables all waste to be handled in the most hygienic way.

However, for particularly remote properties, this is not always an option. In these cases, an alternative drainage solution will need to be put in place, such as a cesspit or a septic tank.


A cesspit, or a cesspool as they are sometimes referred to, is the most basic option for those who are not connected to the mains sewer.

It is a completely sealed tank that sits underground and holds sewage and wastewater generated by the home. A cesspit does not provide treatment of any kind and needs to be emptied regularly by a registered waste handler.

How often the cesspit will need to be emptied depends on the size of the tank and the number of people using it.

The cesspits sitting at the more premium end of the scale are fitted with an alarm. This alarm will send an alert when the tank reaches 75% capacity to prevent overflowing. Where the cesspit does not have an alarm, a schedule should be developed with the waste handler to ensure the tank is regularly emptied.

Cesspits are generally considered a temporary solution and are not usually installed in residential homes. They are, however, used on construction sites and other temporary areas that require some form of waste disposal.

Additionally, cesspits are often used on campsites. Campsites frequently use chemical toilets, which cannot be emptied into septic tanks. The chemicals would disrupt the treatment process, and therefore cesspits are usually the favoured option.

If you plan to install a cesspit, you will need planning permission to do so due to recent changes in regulations. However, if you already have one, there is no need to register it.

The Septic Tank

A septic tank is the most common non-mains waste disposal method in the UK.

Similarly to the cesspit, the septic tank sits underground, collecting sewage and wastewater.

However, rather than being one singular tank as the cesspits is, the septic tank is generally made up of two or three chambers.

The design of a septic tank is simple yet effective. The wastewater enters the tank into the first chamber. It then cleverly separates the liquids and solids, allowing them to be treated.

The liquids are then shifted into a soakaway chamber. A soakaway is essentially a drainage system, which allows the fluids to be distributed evenly into the surrounding soil.

The septic tank needs to be regularly serviced by a waste disposal professional. However, they do not require the same level of attention as a cesspit does, due to their more self-sufficient nature.

Septic tanks use a treatment system, which the cesspit lacks. Meaning, they are a favourable option for many, offering longevity for those who prefer off-grid living.

As with all drainage solutions, individuals need to be extremely careful with what they flush down the toilet and push down into drains.

Sanitary products and nappies flushed down the toilet can block the drain as they would do if the property were to be connected to the mains sewer. Additionally, oil and grease pushed down the sink drain can build up over time, causing severe damage to the septic tank.

Sewage Treatment Plant

A sewage treatment plant is the most complex and effective solution, outside of being attached to the mains system.

Sewage treatment plants look very similar to septic tanks and are buried underground near to the home. However, this more intricate model adds a crucial extra stage to the process.

Initially, the systems work identically. The wastewater enters the tank, and the solids are separated from the liquids. The liquids are then moved through into the second chamber.

The key difference with the sewage treatment plant is that once the liquids and solids are separated, oxygen is introduced to the liquid. The addition of oxygen encourages the growth of ‘good’ bacteria, which purifies the liquid being held in the chamber.

This purified liquid is then passed into a final chamber. The bacteria will settle to the bottom of the tank, ready to be recycled to the start of the chain.

This cleaned water is now sat in the final chamber, ready to be released. The process of purifying the fluid means that it can now be discarded directly into water sources such as streams and rivers. However, it is always best to check with your local environmental agency to confirm you are disposing of the liquid legally.

Although sewerage systems are highly effective, there are some pitfalls in comparison to the two other options. Firstly, they are more expensive. The technology used is much more advanced, so the initial cost will be substantially more.

Secondly, the system requires an oxygen pump, therefore it must be connected to the electricity.

Thirdly, the sewerage plant will require regular servicing. Although the sewerage plant does not need to be emptied as often as a cesspit or septic tank, it does require expertise. The elaborate components of the mechanism mean that regular servicing and maintenance will be required.

How FS Drainage can Help

FS Drainage offers a spectrum of services catering to all sorts of drainage needs.

We offer both cesspit and septic tank services and pride ourselves on giving the best quality help at the most affordable prices. We tailor our services around the needs of your business or home.

For any drainage queries in the South East, contract FS drainage today.

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