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Septic Tank Installation Cost & Prices 2023

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 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£1600
Medium Septic Tank3 -5 days£2350
Large Septic Tank5 - 7 days£3100

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

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:


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. 


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.

Get Pricing on Septic Tank Installations 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.

We work with all the best septic tank installers ready to price your job. Get free, no-obligation quotes in your local area and compare prices using the form below.

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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.