What Is A Septic Tank And How Does It Work?
A septic tank is an underground tank that treats the wastewater from a home that isn’t connected to the mains sewer.
Everything from your toilets, sinks, showers and washing machine flows into the tank. Solids sink to the bottom and form sludge, while fats and grease float to the top and form a crust.
The partly treated liquid in the middle flows out into a drainage field, where it trickles through the soil and is cleaned further. The sludge stays in the tank and has to be pumped out (desludged) regularly.
That’s the short answer. For more details around What Is A Septic Tank And How Does It Work? Below is how each part of the septic tank works, and what homeowners in Staffordshire, Cheshire, Derbyshire and Shropshire need to know.
Who has a septic tank?
Septic tanks are most common in rural properties: farmhouses, cottages, barn conversions and homes on the edge of villages where the public sewer doesn’t reach.
If you don’t pay sewerage charges on your water bill, there’s a good chance your property has a septic tank or a sewage treatment plant.
How a septic tank works, step by step
1. Wastewater flows in - All the wastewater from the house runs through underground pipes into the tank. Most tanks have two chambers, sometimes three.
2. The waste separates - Inside the tank, the waste settles into three layers:
Sludge: heavy solids that sink to the bottom
Liquid (effluent): the middle layer of partly treated water
Scum: fats, oils and grease that float to the top
3. Bacteria break down the waste - Natural bacteria in the tank break down some of the solids. This happens without oxygen, which is why a septic tank only partly treats the waste. It is not a full treatment system.
4. The liquid flows out to the drainage field - The middle layer of liquid leaves the tank through an outlet pipe. Baffles or a T-pipe stop the sludge and scum from escaping with it.
5. The soil does the rest - The liquid enters a drainage field, also called an infiltration system or soakaway. This is a network of perforated pipes laid in gravel-filled trenches. The water seeps out slowly, and the soil filters and cleans it before it reaches the groundwater.
Why the drainage field matters as much as the tank
Most people think of the tank as the whole system, but the drainage field does the final treatment. If it’s undersized, blocked, waterlogged or in unsuitable ground, the whole system struggles.
You may see:
Toilets and sinks draining slowly
Gurgling noises in the pipes
Bad smells around the tank or garden
Soggy, unusually green or flooded patches of grass over the drainage area
Sewage backing up into the property
These are signs to call a drainage contractor rather than wait. A CCTV drain survey can often find the cause without digging up the garden. This is something we can assist with if you are experiencing issues. Please do call us to discuss your needs.
Septic tank rules in England
In England, septic tanks are covered by the General Binding Rules, set by the Environment Agency. The main points:
A septic tank must not discharge straight into a watercourse such as a stream, river or ditch. If yours does, you need to upgrade it, usually by installing a drainage field or replacing the tank with a sewage treatment plant.
Discharges to ground must go through a drainage field built to the relevant British Standard.
The system must be maintained and emptied regularly so it works as intended.
If you sell a property with a septic tank, you must tell the buyer about the system and its condition.
The full rules are on GOV.UK. If you’re not sure whether your system complies, an experienced installer can check and tell you what, if anything, needs doing.
Septic tank vs sewage treatment plant: what’s the difference?
Both treat household wastewater off the mains sewer, but they work differently:
A septic tank separates the waste and partly treats it. It relies on the drainage field and soil to finish the job.
A sewage treatment plant uses electricity to pump air into the tank. This helps bacteria break the waste down much more thoroughly, so the water leaving it is cleaner.
Which one suits your property depends on your ground conditions, where the water can go, and your budget.
How often should a septic tank be emptied?
Most septic tanks need emptying about once a year, but this depends on the size of the tank and how many people live in the house.
Your tank manufacturer’s guidance is the best guide. Leaving it too long lets sludge escape into the drainage field, which can block it, and fixing a blocked field costs far more than regular emptying.
How to keep your septic tank working well
Only flush toilet paper. Wipes, nappies and sanitary products cause blockages.
Don’t pour fats, oils or grease down the sink.
Go easy on bleach and harsh chemicals, which kill the bacteria the tank relies on.
Spread out washing machine and dishwasher loads so the tank isn’t flooded.
Keep vehicles, sheds and trees off the drainage field.
Book regular emptying and have the system checked if anything changes.
Need a septic tank installed, replaced or upgraded?
RC Atkin Contractors installs and replaces septic tanks, drainage fields and soakaways across Staffordshire, Cheshire, Derbyshire and Shropshire.
Martin and the team also handle CCTV drainage surveys, drain jetting and the groundworks that go with them, so we as one contractor can sort the whole job for you.
If your system is old or struggling, or you’re unsure whether it meets the current rules, get in touch for a site visit and an honest assessment.
Frequently asked questions
How long does a septic tank last?
A well-installed and well-maintained septic tank can last for decades. The drainage field usually wears out first, especially if the tank isn’t emptied often enough.
Can a septic tank smell?
A healthy system shouldn’t smell much beyond the lid during emptying. Persistent smells usually point to a blockage, a full tank or a failing drainage field.
Do I need permission to install a septic tank?
New installations usually need Building Regulations approval and must meet the General Binding Rules. Some sites also need an environmental permit. Your installer should check this before work starts.
Can I connect to the mains sewer instead?
Sometimes. It depends on how close the nearest public sewer is and whether a connection is practical and affordable.
Get In Touch
If you have a septic tank that’s old, struggling, or you’re not sure it meets the current rules, we install and replace septic tanks, drainage fields and soakaways across Staffordshire, Cheshire, Derbyshire and Shropshire. Do get in touch to discuss any of your requirements.
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