Bates Environmental Ltd will be pleased to offer you any guidance you require on septic tank installation, maintenance and problems. If necessary, we can arrange to visit your property to conduct a survey. We install new septic tank systems or maintain and repair your existing septic tank system.

For further guidance on septic tanks or for help in diagnosing a problem, please see expandable text below.

How does a septic tank work?

A septic tank will treat wastewater from premises which are not connected to the mains drainage system. It has usually been a large rectangular structure made of brick, stone, concrete or steel buried underground. More modern systems come in the form of a bottle-shaped plastic tank. A septic tank works like a simple sewage treatment plant, except that it is a completely passive system powered entirely by gravity.

Wastewater flows into the tank at one end. Waste material is allowed to settle in the tank and is digested by natural bacteria which must be allowed to breed within the tank. As new water enters the tank, it displaces the water that's already there. This treated effluent drains from the tank’s outlet pipe, normally to a soakaway field drainage system.

Over time partially-decomposed solids build up on the bottom of the septic tank. This sludge has to be removed regularly to make sure the tank continues to work properly and to prevent the soakaway becoming choked. Desludging should normally take place every twelve months.

In the diagram of a traditionally constructed septic tank below, you can see the three layers. Anything that floats rises to the top and forms a layer known as the Scum Layer. Anything heavier than water sinks to form the Sludge Layer. In the middle is a fairly clear water layer. This water contains bacteria and chemicals like nitrogen and phosphorous that act as fertilisers, but it is largely free of solids.


  1. Sewage enters via the inlet T pipe and discharges to the lower of the tank.
  2. Gravity pulls the solids in the sewage to the base and via an aerobic biological action, a scum layer can form on the surface
  3. Effluent (with a very low solids content) leaves via the outlet T pipe. This can then enter a second or third chamber before leading to a soakaway field drainage system.

How do I choose the right septic tank system?

The size of the septic tank system required will be determined by factors such as the number of bedrooms in a home and the rate at which water flows through the soil on the property. Future needs for expansion should be considered as a septic tank system cannot work properly if it is overloaded.

New installations will most likely be of a modern 'bulb shaped' tank that is designed to be very efficient, easy low maintenance and have an environmentally friendly discharge.

Bates Environmental Ltd recommend the installation of a suitable size septic tank from the Marsh Industries Green Filter range, offering the following benefits:

  • No Smell and Foul Odours in the Soil and Grass
  • Low Carbon Footprint
  • No Electricity
  • Kinder to Your Local Environment
  • No Blocked Land Drains
  • Low Ongoing Maintenance
  • A Cleaner Garden for Both Play and Relaxation

How often should I empty or 'desludge' my septic tank?

Contrary to what many believe, there is no "rule of thumb" for how often septic tanks should be emptied. For example, an older system with an undersized tank that is being used by a large family will require much more frequent pumping than a new system used by only a few people.

The general advice from the Environment Agency is that septic tanks should be emptied or de-sludged once per year by an operator licenced for the carriage of waste by the Environment Agency.

A septic tank is considered to be full when 35 percent of the interior space is occupied by solid material, or sludge. The tank will always be full of water, which is what you will see if you open the tank. The solid materials gather at the bottom of the tank and settle there. Eventually, this sludge must be pumped out. If the tank is allowed to fill above 35 percent, there is a risk of solid waste entering the field lines to the drainage field or clogging of the inlet to the tank. Both of these situations can result in major problems and costly repairs.

Bates Environmental will be pleased to advise on the optimum emptying schedule for your particular installation. When you have it emptied, we will be able to tell you the condition of the tank and how full it was. Use this information to help you determine when to carry out the next pumping.

We offer regular inspection, servicing and maintenance contracts for domestic and commercial customers. We are also able to offer an emergency call out service. Our Freephone 0800 0433711 is manned 24 hours a day all year round. We have a large portfolio of customers, domestic and commercial, who return to us time after time because of our prompt, reliable response. Additionally we offer the convenience of being able to order the emptying of your septic tank online:

Order your domestic septic tank emptying online

Order your commercial septic tank emptying online

What maintenance does a septic tank require?

Maintenance of Septic Tanks

Of course, you will already be aware of the need to periodically have your septic tank emptied. If you are unsure of this, please read our Septic Tank Emptying information.

However, there is more to the maintenance of septic tanks than regular emptying ......


Septic Tank Additives

The process involves the use of septic tank additives to ensure that you have an ample amount of bacteria and enzymes in your septic tank to keep the system free from clogging. This will help ensure that your solid waste is being dealt with effectively.


Avoiding Problems

Modern cleaning agents such as disinfectants, bleaches and detergents are designed to kill bacteria. Regular use of these chemicals can upset the biological balance within the septic tank by killing off the micro-organisms that do the work. If you wish to avoid problems such as ......


  • The tank beginning to fill with waste
  • The system beginning to smell
  • The soakaway clogging up with fat and grease and other materials, causing the ground around it to become waterlogged
  • Frequent pump-outs being necessary to avoid the tank blocking and overflowing

....... please read our Septic Tank Dos and Don'ts page!

What is a 'soakaway' and why is it an important part of a septic tank system?

Soakaways are relatively simple structures used as part of a drainage system. Within a septic tank system, a soakaway is the final part of the process, returning waste water to ground after it has been stored to let bacteria breed and break down any pollutants and have the solid elements removed.

Septic tank soakaways may be constructed using several metres of trench lines filled with sand or clean granulated stone (gravel), through which the effluent is distributed along a perforated pipe. Modern soakaway systems are a lot different to the original use of stone.

The size of soakaway system required depends on the number of residents the system is serving, whether it is connected to a septic tank or treatment plant, and how porous the subsoil is. Soakaways are possible when the ground into which they are put is of a sandy or chalky nature, allowing the liquid to drain away rapidly; it is no use trying to employ a soakaway in heavy clay soil. To determine this a porosity test should be carried out, which involves digging test pits and filling them with water. Based on how long it takes for these to empty, it is possible to calculate the permeability of the soil and, therefore, the size of soakaway required.

If the level of the natural water table in the area is of crucial importance. If it rises above the base of the soakaway system, its operation and efficiency may be greatly reduced. In such cases, an effluent pump system may help to solve the problem.


Bates Environmental can supply and install Ezy Drain type soakaway product either as part of a septic tank drainage system, if a survey deems this suitable, or for more general storm/rain water clearance. The soakaway Ezy Drain type technology means that the soakaway can be either permeable textile to allow infiltration, or impermeable geomembrane for storage.

Ezy Drain type soakaway's are light and easy to handle and install. These soakaways are suitable for all applications from light loading.

You must speak to the building control in your own area to ensure the products we are quoting for are suitable for instillation in your area.

What common problems do septic tanks have?

Common Problems with Septic Tanks


Neglected maintenance on the septic tank system

Just because septic tank systems are usually out of sight does not mean that they can be forgotten about. It is vital that certain maintenance operations are carried out.

Firstly, ensure that you have your tank emptied on a regular basis. When this is carried out by Bates Environmental Ltd, our operative will look for any warning signs that your system is not functioning correctly or efficiently. He'll be able to spot things such as water running back into the system from the outlet or the level of the tank being low due to a leak.

The scum and sediment in the holding chambers could build up, reducing the ability of the natural bacteria to cope. This can cause clogging to the inlet pipe or 'H' pipe to the second chamber.


Damage to the baffle walls in the septic tank

Baffle walls may be of single brick construction and are submerged beneath water on both sides. This can mean they have weak or deteriorating mortar and can be damaged during the septic tank emptying process.


Leaking or damaged structure

Septic tanks can be damaged by roots from nearby trees and large shrubs, ground subsidence or from movement of vehicles above / nearby them, causing leaks.

This could affect or pollute local water courses, brooks and rivers as well as the nearby ground water.

If the septic tank system is partially or fully above ground level, or are built into steep inclines and banks, the structure is open to harsh weather conditions including frost which can affect external brickwork. This may involve repair or re-rendering.


Blocked inlet and outlet pipes on the septic tank

Inlet pipes are prone to a build up of grease and fat, which can cause clogging. A poorly designed or damaged system may not have a 'dip' pipe on the inlet to the tank, allowing the scum that forms in the first chamber to cover the inlet and cause a blockage.

The outlet pipe from a tank can become blocked due to root ingress or, in poorly maintained systems, large amounts of solid matter passing through that builds up.


Storm water entering the septic tank

Storm water from roofs and paved / tarmacked / concreted areas should not pass through a septic tank system and should always be handled separately. The workings of the bacteria and enzymes in the tank will be severely impaired. Debris and sediment will be introduced, which may easily find its way through to the outfall pipework, soakaway or filter tank.


Chemicals or detergents affecting bacteria and enzymes in a septic tank

Detergents, cleaners and other products poured into toilets and sinks will affect the way that the bacteria and enzymes operate within the septic tank. You may need to consider an additive to maintain the effectiveness of the bacterial process.


The size of the septic tank isn't coping with what's thrown at it!

A tank installed for a small property, perhaps inhabited by just a couple of people is not going to cope when a two-bedroom extension is added and a family moves in along with a modern lifestyle of washing machines, dishwashers, showers and detergents. Time to upgrade!


Blocked filter media in filter tank

Poor maintenance and general misuse of a system usually means that grease, fat, fibre and sediment passes through the system and clogs any filter system installed, this of course prevents water from reaching the outlet and the system surcharges and floods.


Saturated soakaway on outlet of septic tank

As with the filter systems poorly maintained tanks usually affect the soakaway with grease, fat, fibres and sediment that clogs the sub-soil and prevents water from soaking properly into the ground.

Do septic tanks smell?

Do Septic Tanks or Sewage Treatment Plants Smell?

A well maintained septic tank or sewage treatment plant should not be giving off any unpleasant odours, despite that fact that it is a receptacle for human waste! Septic tanks and treatment plants are designed to contain the naturally occurring odours that will arise as part of the treatment process. If there is an unpleasant smell it could be due to a number of reasons and it is important to investigate the cause .....


Is the tank full and in need of emptying?

This is easily checked and resolved by having it desludges / pumped out.


Is there a clogged vent or is the vent missing altogether?

A vent allows the gases from the sewage to escape and prevent a buildup of toxic and flammable methane gases. Sometimes the vent can become clogged by an overfull tank, a wasp or bird's nest, snow or ice. Check the vent to ensure that the gases are able to escape.It may even be that the tank was poorly installed in the first place and the vent omitted, in which case the gasses (and smells!) will very likely come up through the drains and will make their presence felt (smelt?) in the bathroom, toilet or kitchen.


Has the system been contaminated?

Putting certain things down the toilet or sink, such as very harsh chemicals, grease or fat will interfere with the natural enzymes that work to break down the sewage. When the finely tuned 'eco-system' is disturbed by these contaminants it loses its ability to work efficiently and smell is a likely result.

Cesspools and Cesspits Advice


Cesspools or cesspits is simply a holding tank for untreated sewage. Unlike septic tanks there is very little treatment taking place and they do not drain to a soakaway. Consequently they need emptying very frequently, perhaps every six weeks or so.

A cesspit would be installed, perhaps as a temporary solution, where there is no mains drainage or where discharging into a soakaway is not possible due to unsuitable ground conditions. Examples would also include campsites to handle chemical toilet waste, which would negate the treatment processes that take place in a septic tank or sewage treatment plant.

Cesspools are available in a range of sizes to suit most needs.


Cesspit and Cesspool Problems

A cesspit can give off powerful odours, as it has to be vented to allow the excess sewage gases to leave the tank. Ity should have an alarm fitted to warn that the tank needs emptying. You should NEVER lift the lid to check the level in the cesspit, as the toxic gases can quickly overcome you.

The cesspit can overflow or may leak. Allowing a cesspit to overflow is an offence under the 1936 Public Health Act. If it is allowed to pollute a water course, the Environment Agency may take legal action under the Water Resources Act 1991. This can carry a fine of up to £20,000 and 3 months imprisonment.

If the cesspit leaks you should call out a qualified engineer to remove the waste and clear up the sewage. The cause of the leak should, of course be found and remedied.

Great care should be taken to avoid walking or driving over the top of cesspits. They can cover a very large area under the ground, making them weak as they deteriorate and they can collapse.


Emptying cesspits and cesspools

Cesspits can only be emptied by a licensed waste disposal contractor. Never use anyone, e.g. a farmer, who isn't licensed. There are fines for illegal emptying of a cesspool.

Finally, a cesspit should be installed only when no other system such as a septic tank or sewage treatment plant is possible.

Septic Tanks Dos and Don'ts


By following some simple dos and don'ts you can increase the chances of your septic tank system remaining trouble free and working to optimum efficiency...

Please Do

  • Have your septic tank system professionally fitted in accordance with relevant guidelines and legislation
  • Discharge all your wastewater from your property into the system
  • Find out where your septic tank and drainage field are located
  • Arrange to have your septic tank system inspected regularly
  • Desludge the tank regularly
  • Act swiftly if you find a blockage, clogging or any sign of a problem with your septic tank system
  • Ask for professional help if your are at all unsure - Bates Environmental Ltd will be pleased to advise. Just call us on 0800 043 3711
  • Keep a log or file of any maintenance work you have carried out
  • Ensure that manhole covers are easily accessible
  • Check regularly that any air vents are not blocked
  • Keep the drainage field protected from damage
  • Ensure that other sources of water, like roof and hard standing drains, are kept separate from septic tank systems
  • Try to wash dishes in a dishwasher whenever possible. They are much more efficient at converting fat into soap!
  • Try to use mild detergents, toilet fresheners, fabric conditioners, washing powders and washing liquids in moderation to try not to upset the natural balance of the septic tank. All active ingredients in soap and detergents should be biodegradable and, in normal use, should be safe for septic tanks
  • Use bleaches and disinfectants sparingly as they can kill the friendly bacteria which are essential to make the septic tank work


Please Don't

  • Pour fat, oil or grease down the drains
  • Put paints, solvents or motor oils down the drains
  • Dispose of garden chemicals and pesticides into the septic tank
  • Use the toilet or kitchen sink as a rubbish bin
  • Empty chemical toilets into drains or septic tanks
  • Dispose of nappies, sanitary items or plastic items into the system
  • Drive over the drainage field, cover it with a hard surface or dig into it
  • Block or obstruct any air vents
  • Desludge your tank too often
  • Allow effluent to collect on the surface of the ground
  • Try to climb into or enter a septic tank as gases are produced by the natural treatment process and can be dangerous

If you have a question or need advice regarding your septic tank system, please use our Enquiry form