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Domestic septic tanks: a comprehensive guide

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Domestic septic tanks:
a comprehensive guide

Read our guide to domestic septic tanks and understand what you need to be aware of if you have one on your property.

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Emergency support

We can support with grease trap maintenance and clearing tanks that have become full in the aftermath of severe rainfall. We aim to keep all disruption to a minimum.

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Domestic septic tanks: a comprehensive guide

Domestic septic tanks are often used at rural properties for collecting, treating and disposing of liquid waste where there is no means of connecting to the main, public sewer system.

The containers are located underground in the garden or yard of the property and connect to the household’s plumbing system to collect wastewater from toilets, sinks, showers, and laundry facilities. Homeowners are required to comply with specific regulations when installing and maintaining a septic tank, including regular inspections and treatments.

This guide explores these requirements and other important information for managing the upkeep of a domestic septic tank.

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Domestic septic tanks are underground tanks for sewage

How do domestic septic tanks work?

Septic tanks are watertight containers usually made from concrete, fibreglass, or plastic, and are situated underground at the property. They are designed to store wastewater collected from plumbing, laundry, and other sources, and partially treat before it is collected and transported to larger treatment facilities.

The container is connected to the property by an inlet pipe, through which the wastewater is collected. This is then broken down by naturally-occurring bacteria within the tank into three layers through an anerobic procedure. These layers are:

  • Scum: forms at the top of the water as a result of oils, greases, and fats being broken down
  • Effluent: the remaining material that sits in the middle layer
  • Sludge: heavier particles that sit at the bottom of the tank.

The wastewater then flows through an exit pipe located within the tank where it is transferred to a section within the tank known as a drainage field. The remaining matter is then further broken down by bacteria and the ‘clean’ wastewater filters into the ground to replenish groundwater reserves.

Sludge accumulates over time and a result, needs to be cleared on a regular basis. It is recommended that septic tanks are emptied on a yearly basis, depending on usage, and larger tanks emptied once every three to five years, though it is important to check on a regular basis. The more sludge that accumulates, the less effective the tank becomes and a blockage becomes more likely.

Maintaining domestic septic tanks

It is the responsibility of the homeowner to ensure a domestic septic tank remains in good working condition. Knowing the inner workings of a septic tank ensures that problem areas can be identified before they escalate into more significant issues.

The most common areas of maintenance to monitor include:

  • Inspecting the tank for damage or leaks
  • Clearing solid particles (sludge) on a regular basis to prevent buildup
  • Maintaining the drainage field to prevent it from any clogging or becoming blocked

In addition, it is important that no harmful chemicals enter the tank system, as these can find their way int0 the groundwater reserves. Large volumes of water, too, can cause issues within the tank and the wider network.

Scheduling regular inspections and clearances, like the services we provide at William Gilder Group, allows you as the homeowner to protect yourself from costly and indeed, dangerous, situations, and benefit from a system that flows smoothly and effectively. Regular pumping also maintains a suitable level of bacteria, which is vital for the anaerobic processes mentioned earlier.

Decantation and sedimentation

Decantation and sedimentation are two vital activities that take place within a septic tank and the treatment of liquid wastewater. They are also important parts of the overall maintenance of a tank.

The former refers to the settling of heavier particles within the wastewater collected in the tank. The process of sedimentation involves the further breaking down of these particles through gravity and therefore, aiding the treatment process.

A vehicle for collecting waste from domestic septic tanks

Signs that your septic tank may be full

There are several signs that can alert you to a full septic tank. Before we look at them in more detail, it is worth remembering that ‘full’ actually has a few different meanings, which will determine the appropriate action to take.

Normal level: This means the septic tank is operating at the level it was designed to hold. Wastewater will flow through the system as intended and the tank will empty when it is pumped.

Sludge build-up or sludge accumulation: This is a common problem encountered by most domestic septic tank owners. Sludge, the heavy waste particles that fall to the bottom of the tank, can become trapped and needs to cleared in order to maintain effectiveness. If left unattended, the issue can lead to the tank reaching capacity more quickly and its effectiveness greatly reduced.

Overfilled tank: The tank will be unable to take in any further wastewater, and back up into the overflow tank. Eventually, the water will leak out and cause further risks to health and property.

Now let’s examine the signs that your septic tank is full a bit closer.

  • Water pooling: one of the first signs to look out for is pooling around the drain field or the area of your property where the tank is located, especially after a period of prolonged dry weather. This could mean that the tank is overflowing.
  • Slow drains and sewage backup: if you notice that your sinks are taking longer to drain, or issues when flushing the toilet, you may have a clog that needs clearing. This can be cleared simply by using a septic-friendly drain cleaner, but if the problems persist, you might need specialist cleaning.
  • Sewage odours: it might seem obvious, but an overfilled septic tank will start to produce a foul odour if left untreated. The smell could also be an indication of a leak, so it’s important to check the tank immediately should you (or your neighbours) start to notice it.
  • Unusual sounds: gurgling water is another indication that your septic tank is at capacity. If you notice these are happening continuously, you may need to call in professional clearing services.
  • Lush lawns: though it might seem like a good thing, grass that is unusually lush could also be a sign that a septic tank is full. Areas of grass around the tank will appear much healthier than the rest of the lawn, even though it will have been growing under similar conditions, so pay close attention to these signs.
A full domestic septic tanks

The regulations for domestic septic tanks

It is vital that homeowners keep up to date with the regulations for having a domestic septic tank on the property, as set by the Environment Agency. These are known as general binding rules. Major changes to these regulations were introduced in 2015, with additional regulations brought in between 2020 and 2023.

As of January 2023, it is now illegal for newly-installed domestic septic tanks to discharge to surface water, such as streams and canals. Upgrades to existing septic tanks that had previously discharged to surface water needed to have been in place ahead of a 1st January 2023 deadline.

Property owners now need to have a domestic sewage treatment plant installed alongside the septic tank itself. This ensures that wastewater effluent – the middle layer of wastewater – is treated to a much higher standard and is ‘cleaner’ before being filtered out of the tank system.

Before commencing the installation of a septic tank, property owners need to be compliant with specific planning permission regulations set by the local council. Naturally, these can vary according to the property and the locality, but as a general rule, septic tanks must be at least seven metres from a habitable property and within 30 metres of an access point to ensure it can be emptied easily.

Additional requirements need to be met to protect areas of conservation and sites of special scientific interest, or SSSIs. For example, discharges cannot be made into an enclosed lake or pond, nor can they be within 500 metres of a Special Area of Conservation (SAC) or within 50 metres wells and springs that supply water for domestic or food production purposes.

The latest general binding rules guidance for domestic septic tanks is available on the GOV.uk website here.

Choosing the right domestic septic tank for your property

Deciding on the right type of domestic septic tank is dependent on a number of factors. Generally speaking, a tank that has a capacity between 2 700 and 3 400 litres (roughly 600 – 750 gallons) is suitable for a one to two bedroom property, with larger houses ranging up to around 5 700 litres, or 1250 gallons.

This also depends on water usage, which can vary based on how many people live at the property and the number of facilities such as bathrooms, laundry and dishwashers.

It is also important to factor in the soil on which the property is situated, as different soil types are more effective at drainage than others. As a general rule, sandy loam soil is considered to be one of the best types for domestic septic tanks, whereas clay tends to be one of the least ideal due to its high water retention.

Domestic septic tanks come in a variety of shape designs and as we mentioned previously, are typically constructed from concrete, fibreglass, or plastic. These attributes, too, need to be carefully considered. Concrete domestic septic tanks, while durable, can be difficult to install, whereas plastic is much lighter and makes the installation process smoother. Fibreglass is highly resistant to corrosion and watertight, so again, is an ideal alternative.

Domestic septic tanks and sewage treatment plants: the difference

Though they are both part of an off-mains sewage system, septic tanks and sewage treatment plants are not the same.

As we’ve explored throughout this guide, septic tanks are underground structures designed to collect and contain wastewater. A sewage treatment plant, on the other hand, is where the treatment takes place. Discharges from a septic tank can be highly polluting if appropriate processes are not followed.

Sewage treatment plants are able to treat a wider range of waste matter and are better equipped to handle large amounts of sewage, with treatment being more advanced than what takes place within a septic tank. Both, however, are integral for ensuring wastewater is treated and the surrounding environment protected from potential harmful pathogens.

The key components of domestic septic tanks

A domestic septic tank consists of several important components. Understanding how these all function and their role within the tank system is fundamental in preventing blockages and knowing how to properly maintain your tank system.

The inlet pipe

This connects the property’s plumbing system to the tank and allows the wastewater to enter for treatment via the main sewer line. Typically, inlet pipes are made of strong plastic, typically PVC, in order to be resistant to corrosion.

The outlet pipe

This is where the treated wastewater is transferred out of the tank and into the drainage field for further treatment. The pipe needs to be checked regularly for signs of damage and clogging, and further checked by running water through the system to ensure that it flows smoothly, which can be an indication of whether the pipe is blocked.

The dip pipe

This is essential for removing material from the bottom of the tank without disturbing the preceding layers. It is designed with a curved end, which prevents sediments or solids being accidently drawn into the pipe and means that only the targeted substances are removed and therefore, reduces the risk of contamination as the material is removed.

The drainage pipe

This, as the name suggests, is where the effluent wastewater is carried to the drainage field from the septic tank. The treated water is then released into the soil through a wider network of pipes, which prevents the drainage pipe becoming overloaded.

Where is treated wastewater from domestic septic tanks taken?

Domestic septic tanks and sewage treatment plants are key for keeping harmful contaminants from sewage out of the UK waterways. When a septic tank needs emptying, the wastewater is transported to approved facilities by a specialist waste collection firm such as William Gilder Group, in vehicles that are specifically designed for containing non-hazardous waste.

It is the collection company’s responsibility to ensure the liquid waste is taken to a suitable treatment facility. Once the water has undergone further treatment, and meets stringent regulations, it is then released into waterways with solid matter being commonly used in agriculture for soil fertiliser.

Returning wastewater to the environment ensures that it, along with any pathogens, remains out of landfills.

A tanker for collecting wastewater from domestic septic tanks

A summary of domestic septic tanks

In summary, domestic septic tanks are used in properties that are not connected to the main sewar line due to location or any other factor. They are underground tanks commonly made from sturdy materials such as concrete or plastic, and connect to the property through the use of an inlet pipe.

Wastewater collected within the septic tank is broken down by naturally-occurring bacteria, before being filtered out through a series of pipes into a drainage field. It is recommended that a domestic septic tank is emptied on a yearly basis, however it is equally important that homeowners check and maintain the tanks regularly in order to prevent wider issues such as clogs and blockages within the tank’s structure.

When septic tanks become full, the services of a specialist wastewater collection firm, such as William Gilder Group, may be required in order to empty the tank and be sure that there are no blockages. The collected water is transported away for further treatment in specialised vehicles and discharged in accordance with Environmental Agency guidelines.

Get a quote for domestic septic tank emptying

At William Gilder Group, we provide domestic septic tank emptying services across the countries of Gloucestershire, Worcestershire, Herefordshire, and further afield.

We are situated close to junction 9 of the M5 motorway, making us ideally placed to serve these areas and we are proud to have links with operators of treatment facilities around the country.

Contact the team to learn more about our septic tank emptying services, or fill out the form for a quote.

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