Managing your Septic Tank

What are septic tanks and small sewage treatment plants?

If your home or business is not connected to the mains sewerage system or a cess pit, the waste water from your toilets, baths, showers, sinks and washing machines will drain into one of the following systems:


Are underground chambers where bacteria safely break down the waste. Solids sink to the bottom forming sludge and the liquid flows into a ‘drainage field’ where more bacteria treat it as it soaks into the ground. These systems must not discharge to watercourses.


Work in a similar way but use powered mechanical parts to aerate the bacteria. This makes them more effective at treating waste water and means they can discharge treated sewage into a soakaway or directly into flowing water.

Please Note – If not working properly, both systems can release raw sewage, polluting the water in the ground, in rivers and streams, and at the coast. Owners can ensure that their systems are properly maintained by following best practice guidelines, and new General Binding Rules introduced in 2015. These rules must be complied with by law.

Get to know your system

Where is your tank? A metal or concrete lid should be visible, usually in the ground downhill from your property. Is it shared? Ask your neighbours.

Where does it discharge to? Locate your soakaway. This gravel or grassed area cleans and filters the liquid effluent from your tank. Check your system Check that the soakaway isn’t waterlogged, and that there are no pools of water running in to ditches or watercourses.

Effluent inside the inspection chamber should be clear or pale, and odour-free. Get it emptied regularly All systems need to be emptied of sludge on a regular basis.

Frequency will depend on levels of use, and on how well you treat your system, but having it emptied annually by a registered waste carrier will help to ensure that it functions properly and doesn’t cause pollution.

Don’t upset the balance Using products marked as ‘suitable for septic tanks’ or ‘environmentally friendly’ will keep the bacteria in your tank healthy. The bacteria break down your waste, so the tank could cause health risks and environmental problems without them.

Avoid harsh chemicals like bleach, caustic soda, disinfectants and anti-bacterials, and use cleaning products and detergents sparingly.

Domestic sewage systems can’t remove phosphates from the effluent, so using phosphate-free products will help to protect your local rivers and streams.

Bin your waste Household waste can block or damage your system and should be binned instead of flushed. Kitchen towels, ‘flushable’ wipes, tissues, cotton buds, nappies and sanitary items will all block your tank or pipes leading to expensive repair bills.

Oils, fat and grease will solidify and block pipes and soakaways. Use a kitchen sink strainer to prevent food waste filling up your tank, or it will need to be emptied more frequently.

Paints, solvents and chemicals can kill your tank bacteria and should be disposed of at a civic amenity site. Medicines can also kill your bacteria.

Don’t over-water! Large volumes of water can overwhelm your tank, flushing out untreated sewage. Ensure that roof gutters carrying rainwater aren’t connected to your system and avoid running dishwashers and washing machines several times in one day.

Fix Faults Gurgling pipes, discoloured effluent, odours, foam, a swampy soakaway, lush grass growth, and sewage fungus (that looks like grey cotton wool) in local waterways can all indicate that your system isn’t working properly. The most common problems are that tanks are full and need to be emptied, or that pipes are blocked – these can be cleared with boiling water or drain rods. Problems must be fixed immediately, preventing pollution, health risk, and escalating repair bills. Accredited engineers can fix more serious faults and carry out servicing.

Follow the law Calculate how much your system is discharging at – if you discharge more than 2,000 litres of treated sewage / day into the ground or 5,000 litres to flowing water, you will need a permit. If replacing or installing a new system, choose equipment that meets British Standard BS EN 12566 and speak to your local council to check that it will meet planning requirements and building regulations. You will also need to contact the Environment Agency to find out whether your new system will need a permit.