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Everything you need to know about septic tank systems

Everything you need to know about septic tank systems


Many buildings utilise a septic tank in order to treat sewage. The basic principle is to reduce the presence of any solids in the waste. They generally do not treat waste as efficiently as more modern methods, such as wastewater treatment plants.

In a standard tank design, sewage flows into the first chamber of the tank. Over time, sludge from the sewage settles at the bottom and scum floats to the top. Sludge is mostly bacteria and fecal matter, while scum consists of fats, grease and oil.

Effluent is what people call the watery component between the sludge and scum. The tank requires the emptying of sludge periodically. It is possible to drain the effluent into a drain field – which are generally underground. This is the fundamental design of a septic tank.

Types of septic tank

The design of the septic tank is relatively similar between types.

However, there are many variations. For example, some septic tanks are part of a domestic sewage system but operate alongside other forms – such as wastewater treatment plants. Wastewater treatment plants provide further treatment to reduce pollution.

People differentiate types of septic tanks by the design, or technological technique, they use or the material of which they are made.

The main materials people use to construct septic tanks are:

Concrete septic tank

The most common material that people use in the construction of septic tanks is concrete. Concrete has many desirable characteristics for the treatment of sewage.

The advantages of a concrete tank include:

  • Long-lasting: As the septic tank will be underground any kind of maintenance, repair or replacement can be challenging. The fact that concrete lasts for an extremely long time, at least 20 years, is a distinct advantage.
  • Large capacity: Concrete tanks can be made very large. As a result of their size, concrete tanks require less frequent emptying. With less need to empty the tank the less maintenance overall, which is an appealing characteristic of this design.
  • Watertight: One of the desirable things about a concrete septic tank design is that they are watertight. Concrete tanks, and concrete in general, is watertight. Watertightness is a crucial characteristic for any kind of sewage system so they can be a very good choice.

Concrete septic tanks are a durable and long-lasting design, they are also relatively simple to install because concrete is extremely durable. This durability also means that concrete tanks can withstand ongoing maintenance.

Plastic septic tank

Plastic is another material that people use to manufacture septic tanks. Plastic tanks have advantages that can help facilitate effective sewage treatment.

These advantages include:

septic tank treatment
  • Cost: Sewage treatment can be very expensive and a plastic tank provides a cheaper material. It is cheaper because of it’s lightweight nature and the ability to manufacture it easily.
  • Durability: Plastic has a flexibility and resistance that makes problems such as corrosion less of a problem. Plastic is resistant to many forms of chemicals and will also resist cracking or rust.
  • .Temperature resistant: Plastic may be a good choice in locations where temperatures change dramatically. The resistance to both heat and cold can make plastic a versatile choice.

Opting for a plastic septic tank design provides a low-cost option that resists many environmental challenges. A lower cost and simpler construction process can make the undertaking of upgrades or maintenance on the tank more manageable.

What is the best septic tank?

The short answer is that there is no best. Drawing up a viable plan, depending on the land and surrounding areas groundwater level, is an essential first step. While concrete tanks are long-lasting they are expensive. Similarly, plastic tanks are cheaper but may require more maintenance.

If you need some assistance with the design on your septic tank installation, or you’d like to add a wastewater treatment plant, then don’t hesitate to contact us. With extensive experience across the UK we are experts in the field.

It is also possible that people looking to buy a property will consider the condition or design of the septic tank before making an offer. For more information on this you can read our guide on ‘Selling a House with a Septic Tank’ here.

Additional disadvantages of each include:

  • Plastic: Plastic tanks may puncture during installation. Improper installation may also lead to issues with the tank shifting in the soil in future.
  • Concrete: Machinery is necessary when installing a concrete tank. Repairs and maintenance can also be extremely challenging to complete.

The choice depends on a person’s individual circumstances. There are also a few other less common materials that people use in septic tank design, such as steel or fiberglass.

There was also an older Victorian design using bricks, which was the standard in the UK at one point but now is not common and is largely obsolete.

Septic tank design varieties

Once the wastewater comes out from the building, the basic principle of a septic tank is fundamental to most constructions. However, there are some variations that can differentiate their designs.

2/3 compartment septic tank design

One of the ways that basic septic tank designs can differ is in how many compartments they have. Every tank, by definition, has at least a single compartment.

However, some will have 2/3 compartments. Additional tanks provide more effective treatment. As a result a 2 tank septic system design will provide a higher purification level for the wastewater. Additionally, a 3 compartment septic tank design will provide an even higher level of purification than that.

Drainage system variations

These design variations are mostly in how the outlet distributes the wastewater. Sometimes these differences can be quite subtle. Examples of different septic tank drainage systems include:

  • Drip distribution: A thin tubing system just below the surface drips the wastewater gradually across the drainage area.
  • Gravel drainfield: A commonly seen and quite old design, this filters wastewater through gravel toward the soil.
  • Sand filter system: The wastewater goes from the tank to a pump and then through a layer of sand to filter back into the earth.
  • Gravel-free drainage: Here the effluent flows through plastic pipes to crescent moon shaped chambers.
  • Mound septic systems: The tank pumps wastewater into a perforated pipe buried between a layer of gravel and sand, on top of which goes earth. They usually grow vegetative cover.

Other examples of drainage system variations for septic designs include evapotranspiration, where the effluent is ventilated through soil, and a wetland system that imitates the environment of a natural swamp.

Septic tank construction and design options

As you can see, there are many different types of septic tank design available. Each one has its own merits, depending on a person’s individual situation and needs.

To get started on your septic tank system get in touch with us today. Or, if you’re not sure where to start, feel free to view our services or contact us for some friendly advice.