Cost Guides

Septic Tank Cost Breakdown

Written by  John Davies
Last updated: August 21, 2023
Septic Tank Cost Breakdown

If you need a septic tank, it’s likely you can’t or will not use public sewer systems. The circumstances could be that it is a construction site, youth camp, house in the country or cabin in the woods. Or the situation is that you are in the middle of the city, but have decided not to use the main sewer system.

Whatever the reason, with public sewers out of the equation and you cannot release wastewater (aka sewage or liquid waste) into waterways or open fields, a septic tank is essential.

A private drainage system is a necessity as it offers a way to manage sewage so it doesn’t contaminate the soil, air and water in your surroundings. If you don’t put a system in place, that area will become unhealthy and potentially harmful to vegetation, animals and person alike. Additionally, you could also violate building regulations and environmental laws, risking tens of thousands of pounds in fines.

With this in mind, you are looking at this article for tips on septic tank installation costs. It is expensive, especially compared to the cost of using public sewage systems. You are looking at £1000 to £3,500 in costs, depending on factors that we will discuss later.

Still, there are positives to this method. It is a one-off fee for something that will last for decades with minimal maintenance costs. Admittedly, the lifespan and durability depend on the material used and how well-installed the system is.

Once you have read this article, you will have the help you need to get the best price and value for money when having a septic tank system installed. So let’s begin with the cost of septic tanks:

How Much Do Septic Tanks Cost?

Table 1: Cost of installing single chamber septic tanks 

Tank size (litre)Installation cost (£)Installation time frame (days)
4,500 (Small)1,000 – 1,5002 – 3
8500 (medium)1,700 – 2,2002 – 4
12,500 (Large) 2,000 – 2,300 3 – 5

Table 2: Cost of installing multi-chamber septic tanks 

Tank size (litre)Installation cost (£)Installation time frame (days)
Small- 4,5001,600 – 2,000 2 – 4
medium- 85002,000 – 2,5003 – 5
Large- 12,5003,000 – 3,500 5 – 7

The tanks in Table 2 are more expensive because they have multiple chambers, most commonly two.A single-chamber septic tank has one chamber, while a multi-chamber septic tank usually has two. With the latter, the first chamber is usually bigger and linked to the second one by a pipe.

What Does the Average Septic Tank Installation Cost?

Table 3: Average cost per number of compartments/chambers 

Number of chambersAverage cost  (£)
Single 1,000 – 2,300
Multi 1,600 – 3,500

Table 4: Average cost per tanks size 

Size (litres)Average cost  (£)
4,500 (Small)1,000 – 2,000
8,500 (Medium) 1,700 – 2,500
12,500 (Large)2,000 – 3,500

Table 5: Average cost per tank material 

Tank material Average cost (£)
Concrete 600 – 1,000 
Plastic 700 – 1,200
Fibreglass 1,000 – 1,300

What Are the Labour Costs Of Septic Tank Installation?

Labour costs should amount to about £150 to £250 daily. That is the average for every person working on the project, including septic tank specialists and labourers.

However, you will not have to worry about daily rates if you contract the entire project to a professional septic tank installer. They will usually charge you one price for everything. But it is not uncommon for initial costs to change if there are complications.

That being said, don’t approach the contractor yet until you have finished this article as you will be properly informed about getting quotes and deciding what type and size of septic tank will suit your needs.

Labour Costs Of Septic Tank Installation

What Factors Affect The Cost Of Installing A Septic Tank?

Earlier in the article, I mentioned that septic tank installation costs vary depending on certain factors. As long as there are no complications, these are the only cost factors you need to worry about: 

The size of the septic tank

Tables 1 and 2 detail the varying sizes of the septic tank. A bigger septic tank will always cost more as supply costs will increase as will the cost of and space needed for installation. However, that is not necessarily a disadvantage.

Larger tanks take longer to fill up, so you will not need to empty them too frequently. Smaller septic tanks are the exact opposite. If a tank is too small, it will require frequent emptying. This can be frustrating and costly in the long run. However, there isn’t much consequence if it’s too big.  

The right size depends on the wastewater disposal needs of the house or site. To determine the necessary size, try this formula from the British Water Flows and Loads, and BS6297.

Wastewater disposal needs= 150 litres x maximum number of people on the property + 2,000 litres

150 litres= projected daily need for everyone on the property, child or adult

2,000 litres= minimum required by building regulations

Above-Ground vs Underground Septic Tanks

Above-ground septic tank systems are usually cheaper. They are usually smaller and without a permanent drainage system as they are designed for temporary use. You will most likely see them on construction sites, camps etc instead of residential buildings.

On the other hand, underground septic tanks cost more because they are usually bigger and have a permanent drainage system. They also require proper paperwork and labour. As a result, they cost more money but are a much more reliable drainage system.

In other words, an above-ground septic tank is cheaper, but it takes up more space and is only suitable for temporary use. Meanwhile, an underground septic tank is more expensive, but it doesn’t take up space and is far more reliable for long-term use.

Drainage Requirements

According to environmental regulations, all underground septic tanks must have a permanent drainage system whilst ground septic tanks don’t need to. Occasional visits from the local waste disposal site are enough for these but not for underground tanks. As mentioned earlier, it is one of the reasons for the latters’ higher average costs.

That same regulation also states the drainage system to use. You will find only soakaways and drainage fields are allowed. To know more, look up ‘Environmental Agency Septic Tank General Binding Rules 2020’. 

Soakaways used with septic tanks are just like regular soakaways. You dig a hole in the ground and fill it with substances like rubble, rainwater crates or pea gravel to act as a filter. Then the septic tank discharges liquid effluent into the soakaway, where it is gradually released into the surrounding ground.

Note: Effluent is wastewater after being treated in the septic tank.

A drainage field is a field of trenches connected by pipes. The effluent passes through these pipes from one trench into another until fully absorbed into the ground.

These are the two drainage requirements approved by environmental regulations. Soakaways are much cheaper, but they are gradually being used less. Another method of draining a septic system that is being used less is releasing effluent into waterways, like a drainage ditch, drain, canal, river or stream.

That is one more thing you will discover in the regulation mentioned above; it is illegal to release sewage, treated or otherwise, into waterways.

Tank Material

Looking at Table 5, you will see the average cost of installing a septic tank made from three different materials; concrete, plastic and fibreglass. These materials come at different prices, quality and durability.

Concrete tanks are the cheapest. They are also the oldest and are still commonly used today, despite available alternatives. These alternatives include brick and stone and the other two on the list. Concrete septic tanks are usually underground tanks of medium to large sizes with a lifespan of up to 30 years.

Plastic septic tanks are next when it comes to price. They are the least durable of the three but can still last for a decade or two before needing a replacement tank. However, they are not suited for underground usage. Any plastic will crack under the weight of sand and other structure. On the flip side, they are much easier to relocate.

Finally, we have fibreglass septic tanks, the most expensive yet one of the most popular kinds. They are also the most durable, able to last for five decades.


Finally, let’s talk about how location impacts price. For instance, in London, it will probably cost more to install a septic tank compared to other parts of the country. 

How Is A Septic Tank Installed?

After figuring out the type and size of septic tank you need, the next step is to get in touch with a professional installer. This person will come to the site and take the following steps to install your new septic tank:

  • Survey the area: They will conduct a couple of tests, including soil tests, to determine the best type of tank to use and how to best install it properly.
  • Get the necessary paperwork: This includes planning permission and building regulations approval.
  • Design your septic tank: The most important aspect of the design is choosing how to move liquid effluent from the septic tank to the soakaway or drainage field. There are two options. Option one is the gravity system which is best suited for areas with dirt and rich soil. Option two is the pressure system which is best suited for areas with coarse soil or gravel.
  • Excavate the area: Dig a ditch of at least 2 feet in depth to have the underground tank fitted.
  • Install the tank: First, they make a foundation and then install the tank, and then connect it to the other elements of the sewage management system.
  • Inspection: A building inspection officer inspects the project. After approval, all you have to do is cover the septic tank and put it to work.

What About Septic Tank Maintenance?

If the septic tank is installed and maintained properly, it will serve you for decades. The good part is that maintenance costs are mere fractions of the installation cost as discussed here:

  • Emptying: They use a hose to suck out the accumulated sludge for the tank. You should have your septic tank emptied every 1 to 3 years. It is the most important maintenance requirement. Septic tank emptying costs £120 to £350.
  • Pressure washing: You need to do this after emptying. If you empty the tank every year, give it a yearly pressure wash too. Pressure washing costs £100 to £200.
  • Reduce domestic wastewater: By reducing sewage from your kitchen and bathroom, you can reduce the load of the septic tank and the need for emptying. Do this by using eco-friendly washing machines, toilets and showerheads.
  • Watch what you pour down the drain: Avoid pouring bleach, grease and deposit, coffee grounds, paints, pesticides, detergents, cigarette ends and sanitary items into the drain. They affect the bacteria population in the septic tank.
  • Use bioaugmentation: Emptying a tank too frequently can affect the bacteria population. You can boost the with bioaugmentation products. £20 to £40 per year should cover this.
  • Weed the surroundings: Weed to prevent encroachment.

What About Septic Tank Repair?

If well-installed and well-maintained, septic tanks rarely need repairs, but here are some problems you may face:

  • The tanks get eroded, flooded or clogged
  • The pipes break or get blocked
  • It gives off offensive odours

These problems will not cost much to fix, especially if you find and take care of them early. If that is not the case, you may be looking at these three options:

  • Pipe replacement: for broken pipes.
  • Soakaway replacement: costs about £500 to £700.
  • Septic tank replacement: costs about £800 to £2,500 to remove an existing tank, depending on the size and material. However, the total cost could be higher if the surrounding soil has been contaminated. You will have to remove the contaminated soil along with the old tank.


How does a septic tank work?

A septic tank is like a private sewage treatment plant. Wastewater enters the tank, where it is treated with the aid of bacteria. As a result, the harmful components are destroyed, remaining sludge, liquid effluent and scum.

Effluent is the less contaminated, liquid part of wastewater. Scum is the sediment of fat and grease that rise above the liquid effluent. Sludge is the solid that sinks to the bottom. Effluent is discharged while scum and sludge are left behind to decompose inside the septic tank.

Is a Septic Tank the right choice for my home?

It depends. Is there a main sewer? Do you want to use it? If you answer either of these questions with a ‘no,’ you may be better off with your own septic tank. If you don’t want one, you can try alternatives like a mound system, pressurised dosing, sand filter, aerobic treatment system and drip distribution.

How can I save money on a Septic Tank?

Use a concrete septic tank and get the right size. These two tips will keep septic tank installation prices low at minimal risks.

Concrete is durable yet cheap. And by getting the right tank size, you will avoid spending more than necessary on installation and maintenance.

Do you need Planning Permission?

Yes, unless you are using an above-ground septic tank.

You also need building regulations approval. I recommend speaking to local authorities to see if you require anything else.

Can You Install a Septic Tank Yourself?

Yes, but I don’t recommend it. Mistakes can be costly to your pocket and property. It’s best not to install a septic tank yourself unless you are experienced at similar DIY projects and know about the regulatory requirements.

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