What is a Septic Tank?
Septic tanks are commonly found in rural homes, farms and small commercial premises where access to the public sewer system is not available.
Septic tanks collect, treat and dispose of sewage and wastewater from properties that are not connected to the mains sewer network. They are most commonly found in rural locations, villages and isolated properties across the UK.
Understanding how your septic tank works can help you maintain it properly, avoid breakdowns and stay compliant with Environment Agency regulations.
Septic Tanks with a Soakaway (Drainage Field)
This is the most common traditional septic tank system.
How the septic tank itself works
Septic tanks can be constructed from materials such as brick or concrete, while more modern systems are typically made from fibreglass or polyethylene.
Inside the tank:
- Wastewater enters from the property
- Heavy solids settle to the bottom, forming sludge
- Lighter materials such as fats and grease float to the top, forming a scum layer
- The partially treated liquid (effluent) remains in the middle
Most tanks contain multiple chambers and use T-pipes or baffles to prevent solids and scum from escaping the tank.
The tank itself does not fully treat sewage. Instead, it’s designed to retain solids and allow liquid effluent to pass safely to the next stage.
How the Soakaway (Drainage Field) Works
Once liquid effluent leaves the septic tank, it flows into a soakaway (or drainage field), which is essentially a network of perforated pipes laid in trenches filled with gravel.
Here, the final treatment takes place:
- Effluent slowly disperses into the surrounding soil
- Naturally occurring bacteria in the soil break down harmful pathogens and nutrients
- Cleaned water filters safely back into the groundwater
For this process to work effectively, the septic tank must be functioning correctly, and the subsoil must be free-draining and suitable for infiltration.
Why Do Septic Systems Need Regular Emptying?
Over time, fine suspended solids and bacterial biomass pass through the tank and enter the drainage field. Gradually, this causes the soakaway to silt up, reducing its ability to absorb and disperse effluent.
As the drainage field becomes less efficient, effluent drains more slowly, the system struggles to cope with incoming wastewater, and the drainage field may back up. Eventually, the volume of wastewater entering the system exceeds the volume leaving it, which can lead to effluent rising to the surface, pooling or soggy ground above the drainage field, or even sewage backing up into your property.
Septic Tanks with a Soakaway (Drainage Field)
Some older septic tanks discharge directly into a:
- Ditch
- Stream
- River
- Lake
- Pond
These systems no longer meet Environment Agency requirements.
Under current regulations, septic tanks that discharge directly to surface water must be upgraded or replaced with a compliant treatment system, such as a sewage treatment plant.
When Is a Septic Tank Needed?
A septic tank may be suitable for a property that cannot connect to the mains sewer and has enough suitable land for a correctly designed drainage field.
It provides a relatively simple, passive form of off-mains drainage. Wastewater is collected in the tank, where solids and liquids separate, before the partially treated effluent passes into the drainage field for further treatment within the soil.
A septic tank may be appropriate where:
- Connection to the mains sewer is not practical
- The ground is suitable for a drainage field
- There is enough space to install the tank and drainage field safely
- The expected wastewater volume can be accommodated
- The system can be accessed for inspection and emptying
The ground conditions and available space must be assessed before installation. A septic tank cannot discharge directly into a ditch, stream or other surface water.
Why Do Septic Tanks Need Emptying?
The bacteria inside a septic tank break down some of the organic waste, but they cannot remove everything entering the system.
Over time, solid material settles at the bottom of the tank to form sludge, while fats, oils and other floating material create a scum layer at the surface. As these layers build up, the tank has less space available to separate incoming wastewater effectively.
If the tank is not emptied regularly, solids may escape into the drainage field. This can lead to:
- Blocked or damaged drainage pipes
- Slow-draining toilets and sinks
- Sewage backing up into the property
- Unpleasant odours
- Wet or waterlogged ground
- Premature drainage-field failure
- Potential environmental contamination
Many septic tanks benefit from emptying at least once every twelve months, although the correct frequency depends on the tank size, number of users and volume of wastewater produced.
CSG’s Septic Tank Top Tips
- Use biologically friendly household cleaning products
- Have the tank de-sludged regularly, ideally every year
- Don’t allow commercial chemicals, medicines or hygiene products to enter the system
- Don’t use large quantities of biological cleaning products or bleach
- Bacteria in the tank is vital to the biological process
Frequently Asked Questions
Do Septic Tanks Need Emptying - And How Often Should You Empty Them?
Yes. Over time, sludge builds up at the bottom of the tank. If it is not removed regularly, it can:
- Block the drainage field
- Cause unpleasant smells
- Lead to system failure
- Create environmental contamination
Most septic tanks should be emptied at least once every 12 months, although usage levels and tank size can affect this.
Regular emptying prevents costly repairs and keeps the system working efficiently.
What Happens If I Don’t Empty My Septic Tank Often Enough?
If a septic tank is not emptied regularly, sludge builds up at the bottom of the tank and reduces its working capacity. Over time, this could lead to blocked outlet pipes, sewage backing up into your property and costly repairs. In some cases, an overflowing or poorly maintained system can also cause environmental contamination, which may lead to enforcement action or fines from the Environment Agency.
What Maintenance is Needed for Septic Tanks?
Septic tanks are relatively simple systems with no mechanical parts, but they still require routine maintenance to function properly.
Professional maintenance covers:
- Annual emptying (de-sludging)
- Regular inspections for cracks or leaks
- Checking inlet and outlet pipes for blockages
- Monitoring sludge levels
- Ensuring the drainage field remains free-flowing
What Common Issues Should I Look Out For?
Recognising early warning signs can prevent major problems.
Here are some common septic tank issues to look out for:
- Slow draining sinks, toilets or showers
- Gurgling sounds in pipework
- Sewage smells indoors or in the garden
- Pooling water near the drainage field
- Lush, unusually green grass above the soakaway
- Sewage backing up into the property
If you notice any of these signs, it is important to contact a professional promptly. Early intervention can prevent drainage field damage and costly system replacement.
Are Septic Tanks Regulated?
Yes. In the UK, septic tanks must comply with the Environment Agency’s General Binding Rules. Professional servicing helps ensure your system remains compliant and environmentally responsible, but it’s important to stay up to date with the latest official guidance.
Can CSG Empty a Septic Tank with Difficult Access or in a Rural Location?
We understand that many off-mains properties are located in rural areas, and we are experienced in working within those environments. We regularly service septic tanks in rural and hard-to-reach locations. Our fleet of specialist vacuum tankers and equipment is designed to handle narrow access roads, long hose runs and sites with limited turning space, such as remote countryside properties and farms or smallholdings.
What Information Does CSG Need to Provide a Septic Tank Emptying Quote?
To provide an accurate quote, we’ll need the following information from you:
- Property address and postcode
- Approximate tank size (if known)
- Last emptying date
- Number of occupants
- Details of access (distance from parking point to tank
- Any known issues or concerns
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