Septic Tanks Ultimate Guide

Septic Tanks

Septic Tanks Ultimate Guide

Ultimate Guide – As Septic Tanks are a very common and widely used solution to sewage treatment there are naturally many questions. To answer many of the questions we are often asked, we have compiled our Septic Tanks Ultimate guide page which we hope will assist and guide customers in choosing the best solution to suit their requirements. We are often asked many questions such as:

  • What is a Septic Tank?
  • How does a Septic Tank System Work?
  • Do I need a Septic Tank?
  • Would my site be suitable ?
  • What Size of  Tank Do I need?
  • Do I Need Permission to install a Septic Tank? Who do I need to speak to?
  • What is a Drainage Field/Soakaway?
  • What size of Drainage Field/Soakaway do I require?
  • How much does a Septic Tank Cost?
  • Installation Cost?
  • Where to Buy a Septic Tank? 
  • When and Where should I use a Septic Tank?
  • Do we need to upgrade (2020 Regulations)?
  • Our Septic Tank Smells -How do we resolve this? 
  • Septic Tank Maintenance – Do we need to maintain our Septic Tank?
  • Do Septic Tanks Fail? Cause’s of Failure?
  • Do’s and Dont’s – What should we avoid?
  • What is a Sewage Pump Station? Do we need a Sewage Pumping Station? Pump Stations

What is a Septic Tank?

A septic tank is an underground tank made from a variety of different materials. PVC, Fibreglass, Concrete, HDPE. They are used predominately in domestic applications for treating domestic effluent. Septic treatment systems use settling phases and anaerobic processes to treat the effluent. This process only allows moderate treatment levels and further treatment is usually required before the effluent enters either groundwater or a water course. Usually in the form of a soakaway or another for of tertiary treatment. A more basic description would be a multi-chambered tank with an inlet and outlet.

How Does a Septic Tank Work?

Septic Tanks in basic terms separate fluids from solids. The separation of these solids and fluids is done by gravity and separating the tank into 2 or more chambers. A single tank is normally separated with a baffle (central wall). The sewage or effluent is broken down by anaerobic bacteria (bacteria that thrive in an oxygen starved environment). The heavier solids will drop to the bottom of the tank in the first chamber and broken down in a more liquid form through time by this anaerobic process. The lighter particles and grease will rise to the top. The liquid will pass through the hold near the top of the baffle in the second chamber and will eventually pass through the outlet. The whole process with septic tanks relies on gravity doing the work. Unless of course your area of discharge is at a higher ground level therefore an effluent pumping chamber may be required. Advantages

  • No electrical or mechanical parts are necessary.
  • The tanks themselves require low levels of maintenance other than emptying.
  • Relatively low- cost solution ?? (This maybe the case for the tank themselves but take into account the installation procedure before comitting to a Septic Tank System.)


  • Results from Septic Tanks alone are not the best and always require further treatment before discharging to any groundwater or water course.
  • Tend to give off more bad odours in comparison to treatment plants.
  • Heavily rely on ground conditions for discharge.
  • Soakaways and drainage fields are expensive and often require a lot of space to install.
  • Raised Mound Soakaways are also expensive and visually obtrusive.
  • Require emptying far more regularly than other forms of sewage treatment.
  • Now considered an old method of sewage treatment.(refer to 2020 guidelines)

You may wish to Consider a Sewage Treatment Plant instead…..

When would I need a Septic Tank?

You will need one if your home is in an area where you do not have access or a connection to the main sewer system.

How to Size a Septic Tank?

When sizing  you must always follow the British Water Code Of Practice  and Environment Agency General Binding Rules. Sizing A septic Tank You must allow for 2,000 litres of storage and then 150 litres per person. So for example a 3 bedroom house would look as follows: For a 4 Bedroom the calculation would be: 4 Bed= 6PE    2,000 L + (6 x 150L = 900L) Septic Tank required 2900 Ltr

Would my site be suitable for a Septic Tank?

Installation of your system is very dependent on your site suitability. To determine if your site will be suitable for a septic tank and Drainage Field the first thing you must do is conduct a site assessment. If you are installing a Septic Tank you will have to discharge to ground. (2020 Regulations England and wales) This is typically through a soakaway /drainage field or raised mound. On the subject of soakaway systems for septic tanks Crates are not permitted for use under Building Regulations and BS 6297 2008. These “soakaway crates” are for rainwater and surface water applications only. You must check the following before attempting to install your septic tank and drainage field(soakaway)

  1. Make sure it is not in a Groundwater Protection Zone.

This link will show you where the groundwater protection zones are and if your property is affected. You can also contact your local environment agency who will be able to tell you if you are affected.

  1. Perform a Trial Site Assessment Hole dig.

A Trial Site Assessment Hole is a mandatory test when installing a drainage field according to building regulations. This basically involves digging a singular large hole at a minimum of 2 metres where you intend to install your soakaway drainage field. This test hole is used to determine that the water table or bedrock do not reach to within 1m of the bottom of your soakaway pipes. If this test fails you may need to look at an alternative option other than a Septic Tank and Soakaway System. We can help you with your options .

  1. Perform a Percolation Test

A Percolation Test hole is also essential and mandatory as it tells us hole quickly or how slowly water will drain from the intended area. It is basically testing the soil porosity for you intended drainage field. If the results come back and the water drains too quickly a soakaway will not be permitted and again you will need to look at alternative options. Likewise, if the water drains too slowly which tends to be in areas with a lot of clay a soakaway will not be an option. We again can help you with alternative options specific for your needs. We can also carry out TSAH and percolation tests for you or put you in touch with a local specialist in your area. All you need to do is get in touch .

Do I Need Permission to Install a Septic Tank?

The quick answer here is yes you will need permission before installing a septic tank system. If you have or are planning to build a property requiring the use of a Septic tank or package treatment plant you must have planning permission and building regulation approval. You will need to register your Septic tank with one of the below Government bodies depending on where you are based in the UK. England – Environment Agency Scotland – SEPA Scottish Environmental Protection Agency Northern Ireland – Department or Agriculture, Environment and Rural Affairs (DAERA) Wales – Natural Resources Wales Costs The cost of registration will also vary depending on the agency. England Scotland Wales Northern Ireland Small domestic Septic Tanks under 15 population typically cost around £120 – £150 again depending on the agency. Larger systems require a permit or license. We can help with this process for you . Contact Us

What is a Drainage Field/Soakaway?

A Drainage field or commonly known as a soakaway is a layout of rigid half perforated pipes laid in trenches on a bed of gravel, surrounded by gravel and covered with non woven geotextile incorporating a distribution chamber. The drainage field is installed on the outlet side and connected to a septic tank.The purpose of the drainage field is to allow treated effluent from a septic tank to soak into the ground. Drainage fields should also be installed to ensure aerobic contact between the subsoil and effluent – maximum depth 1mtr – max pipe depth 700mm and always 1.2 Mtr above the water table. Drainage fields should only be used where the percolation test results average values Vp are between 12 and 100. A Vp below 12 would allow effluent to percolate too quickly into the ground and above Vp100 would not allow effluent to percolate. In these instances alternative forms of secondary treatment would have to be considered, i.e raised mounds or Tricel Puraflo or Premier Tech Ecoflo units tricel puraflo


What size of Drainage Field/Soakaway do I require?

The size of a Drainage field will be determined by firstly your Percolation test results and secondly by the septic tank size. From your percolation tests you will have a Vp value ( average time taken for water to drain from test holes) From house size and Septic Tank size you will have a (P) value – number of persons The formula used for calculating area required is: Area (A)= Vp x P x 0.25 To calculate length of pipes required depends on width of trench e.g 600mm wide trench calculation would be area (A) / 0.6 Example Vp = 30, P =5 Area (A) = Vp x P x 0.25 :  30 x 5 x 0.25 = 37.5Mtrs 600mm Trench : 37.5 Mtrs / 0.6 = 62.5mtrs Pipe We have created a Table as an example fo the size of Drainage Field required. drainage field calculations We can provide SoaXaway Kits with all the pipe, chambers, fittings and geotextile required for your drainage field. You will also require to lay and surround the drainage field with 20-50mm washed clean stone and cover with non woven geotextile. Stone Requirements Example: 600mm wide Trench x 45omm deep x 1Mtr length would require approx. 0.26Mtr3 Stone Stone costs vary across the UK and can be bought in loose loads or bulk bags. Loose loads may be more cost effective but site and access conditions may be more suited to bulk bags Drainage Field Regulations Drainage fields should always be designed and installed in accordance with Building Regulations and British Water Code of Practice Key Points: Drainage fields are not permitted in Zone 1 Groundwater Protection Areas Minimum 10 Mtrs from a watercourse 50 Mtrs from Groundwater abstraction point 15 Mtrs from a building, 2 Mtrs from Boundary 1.2 Mtrs above Water Table

How much does a Septic Tank Cost?

Although it may seem obvious, you need to know what size of septic tank is required in order to price it accurately. A 2,750L or 5PE Septic Tank Supplied to almost anywhere Mainland UK will cost anything from around £500 +vat upwards depending on the materials and thickness of materials and components used in manufacture. There are many shapes of septic tanks, types of materials and process’s used – fibreglass (spun & pressed) MDPE, HDPE -Roto Moulded, Injection Moulded & fabricated/welded. Every Manufacturer whether it is Roto, Tricel Premier Tech Aqua, Kingspan, Klargester, Harlequin, Marsh, Graf or many of the others all have their own USP’s and will all say their tanks are the best on the market, however it is ultimately the most suitable tank for your application and budget that are the most important factors to consider. Also consider manufacturers warranty. Warranty varies from manufacturer to manufacturer Note: It is also Very Important to consider Installation costs when selecting your septic tank as many tanks require complete concrete surround or partial concrete surround depending on site conditions. Concrete surround/backfill can add anything from £500 to the cost of your septic tank (dependant on size of tank and excavation).


Installation should always be by reputable, experienced installers to ensure the tank is installed properly and in accordance with the manufacturers installation guidelines. Failure to do so may result in any warranty claims being null and void, should the tank fail for any reason.

Installation Costs

Tank Installation costs are difficult to quantify and vary all over the UK as every Installation is very much site specific and various factors affect the cost of Installation. These include Site Conditions, Access, Ground Conditions, Depth of Excavation, Rock Present?, Size of Tank, Tank Installation Guidelines – Concrete Base ? Concrete Surround? Gravel Surround? Time for Installation – Labour Costs, Material Costs – Concrete, Gravel. All important factors to consider before purchasing your tank and yet another reason to buy from experienced Suppliers and Installers. Drainage Field/Soakaway Installation costs will again vary dependant on porosity test results, area required, tank size, material costs and installation time. Drainage fields are an important part of the septic tank system and again should be installed by experienced installers using the correct drainage pipes. Ensure half perforated rigid drainage pipes are used NOT land drainage coil and the drainage field is installed in accordance with building regulations H2 1.39

Types of Septic Tanks.

Septic Tanks come in various forms shapes and sizes but in essence they will all do the same job. Two main differentiating factors are the materials the tanks are made from and the installation guidelines. These can have a positive or negative effect on the installation costs of the tanks. Xoli are proud to offer the below;

Roseptic HDPE  by Roto Group Available in sizes from 3000 Ltr to 50,000 Ltr.

Septic Tanks

Vento HDPE  by Tricel Available in Sizes form 3000 Ltr to 5000 Ltr

Conder HDPE Millenium by Premier Tech Aqua Available in sizes from 3,000 Ltr to 10,000 Ltr

Conder HDPE septic tanks

Septic Tanks Maintenance

Maintenance is very basic much like the tanks themselves. Typically a septic tank would need emptied once a year. If you would like a costing on this service we can help you out . FOGS or Fats, Oils and Grease can also cause major issues with your septic tank system. We always recommend installing a Grease Trap before your septic tank or sewage treatment system to eliminate this potential issue. We offer a variety of grease traps in many shapes and sizes to suit your specific application

– Above Ground – Underground – Under Sink.

RoGre                                                              Romast Rogre Grease SeparatorsAbove Ground Grease Traps

Do’s and Dont’s

We also have a guide that is helpful for what you should and shouldn’t flush into your septic system .

Do we need to upgrade (2020 Regulations)

New Regulations come into force in 2020 for Septic Tanks in England and Wales. Septic Tank Regulations 2020

Septic Tank Smells

Is your Septic tank  smelling or causing you problems? There can be many causes for your tank to be smelling badly.

  • Excessive Detergents or Cleaning Chemicals being flushed through your system.
  • Poor Installation
  • Lack of Maintenance or system not being emptied at regular intervals
  • Broken or Loose lids fitted
  • Fats, Oil and Grease (FOG) entering the system
  • Lack of ventilation or no ventilation – The most common problem

According to Building Regulations H2 1.21; “Septic tanks should prevent leakage of the contents and ingress of subsoil water and should be ventilated. Ventilation should be kept away from buildings.” Your Septic must be vented on the outlet pipe from your tank and vented through the soil stack in your property as long as the vent exits above roof height. This allows gases to escape from the system and is essential. There are many vents readily available, however buying and installing the correct components to allow ease of installation can be difficult. Xoli offer a fantastic product to reduce and eliminate any odours from your septic tank system.

This product is our septiXvent


Our Xoli TV youtube channel also has a great tutorial on how to install the septiXvent.

Septic Tanks Failures

FOGS or Fats, Oils and Grease can also cause major issues with your septic tank system. We always recommend installing a Grease Trap before your septic tank or sewage treatment system to eliminate this potential issue. We offer a variety of grease traps in many shapes and sizes to suit your specific application . Grease Traps Emptying – Your septic tank may also require emptying and this could be causing issues with smells. We have can help with emptying your septic tank simply give us a call on 01236  796437 or via social media. Twitter icon, facebook icon, linkedin icon. Drainage Field Failure – If you have had your septic tank and soakaway drainage field installed for a number of years it could be that your soakaway or drainage field may need replacing. They typically have a lifespan of around 10-15 years. Other issues can occur with septic tanks and therefore cause problems. Things like collapsed baffles or water ingress. We at Xoli can help find these problems for you by way of an inspection. After carrying out the inspection we will offer the best solution that meets your needs .

Ultimate Guide

We hope our Septic Tanks Ultimate guide has answered your questions, If not and you have other questions, do not hesitate to call us on 01236 796437 Contact Xoli