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The Ultimate Guide to Septic Tank Installation: Cost, Process, and Tips

19th October 2023

Septic tank installations can be major projects that require careful planning and execution. It’s important to make sure this is done correctly as improper installation can set you up for unexpected repairs that may cost a considerable amount to put right. In this comprehensive guide, we'll cover everything homeowners need to know about the costs, varying factors that affect such costs, the installation process and tips for an effective septic tank setup. Whether you're installing a new drainage system or replacing an existing one, knowing and understanding these key factors are crucial. Here at Cotswold Drainage, we offer professional installation, maintenance and repair services for septic tank systems across the UK. Get in touch with a member of our team for a full breakdown of the areas we cover and how we can help you today.

Cost of Septic Tank Installation

Septic tank installation costs vary from job to job. We know this can cause some uncertainty for property owners and investors when trying to budget finances. To help alleviate some of those uncertainties here are some factors that affect the overall cost of your septic installation.

Size and Type of Septic Tank

Both the size and type of septic tank system to be installed will affect the price. Larger tanks and advanced treatment systems carry higher price tags. Whilst you should always opt for the correct sized tank to suit your household needs, this is an important factor to bear in mind.

Soil Conditions

The condition and quality of the surrounding soil can also significantly impact septic tank installation costs. Soils that absorb more water, such as clay or silt, can prove to be troublesome and may require additional groundwork to make the area more suitable, increasing overall expenses.

Location and Permits

The location of your septic tank system and its proximity to larger bodies of water matter for permit requirements. In regulated areas or those near wetlands, special construction permits and independent inspections are often required to ensure compliance, whilst preventing the contamination of sensitive ecosystems. Homeowners and property owners should research the necessary permits and inspections required before planning the installation of their septic tank.

Septic Tank Installation Process

Installing a septic tank can be a complex process, one that is best left to the professionals. For more guidance, we have summarised this process, step-by-step to help ensure everything runs smoothly from start to finish.

Step 1: Site Evaluation

A site evaluation helps assess the suitability of your intended location, which usually includes a percolation test that calculates the soil's absorption rate. Once the soil suitability is confirmed, it’s time to determine the ideal location based on your specifications, tank size, piping layout and other varying factors.

Step 2: Permits and Regulations

After the initial site evaluation, the next step would be to research the relevant permits and inspections for your septic system installation. The permit application and approval process can be between 1-2 weeks, and it is important to wait for this approval before starting any groundwork.

Step 3: Excavation and Tank Placement

After marking out the approved area and placement of your septic tank installation, it’s time to dig trenches for the tank itself, piping, electrical wiring and drainage. Follow the relevant guidelines for depth before lowering your tank and the other components into place. Remember to divert the drainage and runoff away from the system.

Step 4: Connecting the System

Now it’s time to connect your household plumbing system to your septic tank. Be sure to test the watertightness of your septic tank outlets to the distribution box and leach drains.

Step 5: Inspection and Testing

The final stage is to inspect your septic tank, testing it out for proper functionality. Also, inspect the surrounding areas for leaks and test out the connected pumps and controls.

Tips for Cost-Efficient Installation

Although installing a septic tank can be a significant investment, by adopting some of the tips and practices below, you can reduce some of the associated costs.

Choose the Right Tank Size

Work with professionals and septic tank experts to choose the right-sized tank for your household and the level of waste produced. Take into consideration the number of occupants and the average amount of water usage. Oversizing your septic tank can lead to higher upfront costs and may cause further issues down the line, whereas under sizing will result in your tank filling up quicker, increasing the frequency of pump-outs.

Soil Improvement Techniques

Does your home have highly dense and solid soil in the summer or soggy soil that takes forever to soak in the winter? If the answer is yes, you likely have clay soil which is unsuitable for septic tank systems. Try installing a sand leach bed or a gravel trench system to enhance drainage without busting the budget. While not ideal, these solutions are far more affordable than trucking in all new soil.

Get Multiple Quotes 

Pricing can vary widely between professionals for septic tank installations, so getting at least three to four quotes for your project is an easy way to find the best price. However, don’t just look at the bottom line as different companies use different materials and machinery. It’s always a good idea to look at reviews and personal recommendations to make sure you select the best person for the job.

Regular Maintenance for Longevity

A key way to get the most value from your investment is through proper maintenance. By having your tank inspected, emptied and cleaned on a regular basis, you can significantly reduce the chances of breakdowns or failure that lead to costly repairs. This also increases its lifespan as a well-maintained septic tank can last for years to come.


We hope this guide has helped shed light on the installation process and costs for septic tank drainage systems. Arming yourself with the right information from the beginning helps avoid setbacks or mistakes that can eat further into your budget. If you have any further questions on septic tank installations or drainage systems, feel free to give us a call or fill out our simple contact form. Here at Cotswold Drainage, we've installed countless systems with decades of experience under our belts. We're happy to offer our expertise and help in any way we can!