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Septic Tank Installation Cost & Prices 2022

For those who live in more rural areas, a septic tank is an important part of reality.

The absence of mains sewage in remote dwellings means homes need to have their own system for draining and treating wastewater.

When it comes to installing or replacing a septic tank, there are many factors that can affect the price.

This article will cover what you can expect to pay for a septic tank installation, factors that affect its cost and common questions around installing a septic tank.

Average Septic Tank Installation Cost

The cost of the tank itself is between £700 and £1,200, depending on the size.

For installation, a septic tank specialist will charge between £150 and £250 per day and installation generally takes between 4 and 7 days, depending on the size and where it is installed.

You can expect the costs of installing a septic tank to be roughly as follows:

Tank SizeInstallation DurationAverage Cost
Small Septic Tank2 - 4 days£1500
Medium Septic Tank3 -5 days£2250
Large Septic Tank5 - 7 days£3000

If the septic tank is installed above ground, installation takes much less time as there is no excavation required. You’re looking at an average labour cost of £200, plus the tank, meaning the total cost will be between £900 and £1400. 

Factors That Affect the Cost of Installing a Septic Tank

The average cost of installing a septic tank will vary to a reasonable degree according to a number of factors. We’ve listed them below:

Size

The tank size is one of the significant variables affecting the price.

Although smaller septic tanks have a cheaper initial price, if you have a larger household, the tank will need to be emptied more frequently and therefore, increase maintenance costs.

Septic tanks are not only used for sewage, but also for the water from washing machines, dishwashers, sinks and showers. All the water from your home will drain into the septic tank, so it’s important to have the right size.

It will save you more money and time in the long run to have a tank that is too large than one that is too small. 

Underground vs Above Ground Septic Tank

Installation costs are generally higher for underground septic tanks due to the excavation required.

Large septic tanks are normally designed to be fitted underground, which is often the only choice of location on smaller sites where space is limited.

If you are having a small system installed, it can be more cost-effective to leave it above ground. However, the maintenance costs incurred by more frequent emptying can render the price difference obsolete. 

Drainage Requirements

Below-ground tanks require a draining system, which is an additional cost.

These tanks often have a soakaway, which filters some of the wastewater out into the surrounding earth and reduces the need for emptying. It’s worth noting not all installation sites are suitable for a soakaway system.

You’ll need to have this checked out before and if the area is not adequate for soaking, make sure to factor in the cost of installing a complete draining system. 

Tank Material Used

The better the material quality, the higher the costs. It can be worth opting for a better quality though in order to increase it’s lifespan.

For example, concrete tanks tend to cost less initially, but concrete tanks need to be replaced fairly regularly.

On the other end of the scale, a septic tank made of high-density polyethylene will cost much more to buy, but is more cost-effective long-term as it will last much longer. 

Location

Labour costs in London and the south of England are generally more expensive than elsewhere.

If the contractor needs to travel beyond a certain radius, then they may add an extra fee on top. Since many homes requiring a septic tank tend to be in very rural locations, it’s best to check with a contractor whether your property is outside the radius.

Removal of Existing Tank

There will be extra labour costs if you have an existing tank that needs to be removed and disposed of first.

Although it is possible to save yourself money by hiring a digger yourself, it’s best to contact a professional to carry out the installation in order to avoid any complications.

What is a Septic Tank?

A septic tank is a waste water treatment system composed of a watertight container made of fibreglass, concrete or plastic.

It treats household wastewater produced by bathrooms, kitchens and laundry systems using biological decomposition and drainage processes.  

The septic tank is normally composed of two chambers separated by a small gap which allows the liquid to flow between them.

The first chamber is known as the “settling” chamber, where the sewage is separated and the solids fall to the bottom while the scum rises to the top. The liquid effluent then flows into the second chamber and then out of the tank. 

There are two types of septic tanks:

  • Overground septic tanks: tend to be smaller and cheaper to install but require emptying more frequently. 
  • Underground septic tanks: tend to be larger and more expensive to install but doesn’t require as much emptying.

Underground septic tanks will need to have a very large hole dug, much larger than the tank itself, because an underground tank needs to have foundations built before it can be installed and also needs space for a surrounding area of gravel which comprises the soakaway for overflow. 

Some areas have restrictions on certain types of septic tanks so make sure to contact your local council before going ahead with installing one. 

How Do Septic Tanks Work?

Septic tanks work by retaining the wastewater from household plumbing until it naturally breaks down by way of bacterial decomposition.

The sewage stays in the septic tank until it separates, with the solids settling and the liquid effluent eventually being safely drained into the surrounding ground via the soakaway, once it is no longer contaminated.

The solids remaining in the tank eventually decompose over time thanks to naturally-occurring bacteria. 

Although most of the sludge in the tank will break down, there is always a low level of residue which will build up over time and cause the need for emptying the tank.

A contractor hired to empty a septic tank will remove the solid residue but retain the watery effluent as this contains the natural bacteria which break down the sludge and cause the tank to work properly. 

Discharge from a septic tank is still lightly contaminated and requires treatment. It is illegal for septic tank discharge to flow directly into a drainage ditch or watercourse and it must instead be treated via a drainage field or a specifically constructed wetland.

If these options are unavailable, a Sewage Treatment Plant must be installed. 

What is Involved in Installing a Septic Tank?

All septic tanks need to be replaced at some point or another and the regularity with which they need replacement depends greatly on the quality of the material.

Concrete tanks, for example, require more frequent replacement than those made of fibreglass. 

If you are replacing an existing septic tank, the process is pretty simple. First, you must empty and clean the old tank to remove the risk of contamination before taking it to a waste disposal site.

Installing a septic tank where there has already been one is straightforward since the system is already in place, although it’s a good idea to take the opportunity to have the drainage system checked while the area is empty. 

Having a septic tank installed for the first time requires more work. Depending on whether you go for an over or underground system, you may need to excavate the area to create a hole big enough to contain the tank, lay a solid foundation and put in the gravel soakaway drainage system.

Installing an above-ground system is much less complicated and takes less time meaning it is generally a cheaper job. 

Can You Install a Septic Tank Yourself?

Septic Service

It is true that some parts of septic tank installation can be done using DIY methods but this is only really advisable if you have some experience and the relevant materials.

Removing and disposing of an old tank can be dangerous and it is essential to properly empty and decontaminate it.

Equally, the correct positioning of a new septic tank is essential as messing this up can result in a whole host of problems from blockages to a tank that won’t stay underground. 

Besides, you’ll need approval and planning permission to install a septic tank and your area may be subject to regulations that would make DIY installation very complicated.

It is, therefore, better to hire a professional contractor to replace and/or install a new septic tank.

Do You Need Planning Permission?

The short answer is yes.

You’ll need planning permission from your local council regardless of whether it is installed at your home or a business location. There are strict regulations that must be followed.

Get Prices on Installing a Septic Tank Near You

We’ve done our best to give you a good idea of what you can expect to pay for a septic tank installation.

However, our guides are not a substitute for a fixed quote specifically for you.

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About the Author

Alex Johnson is a qualified quantity surveyor and writer with a passion for conducting original research and uncovering the true cost of jobs. His cost data has been referenced by EDF Energy and the Scottish Government.