Septic tank maintenance: what you must do and when

A septic tank has no moving parts, which is why owners forget about it until something goes wrong. Most failures, though, start with a missed emptying or the wrong things going down the drain. A little routine prevents the expensive end of the job: a flooded drainage field and a replacement.

What the rules require

In England the Environment Agency’s general binding rules make maintenance a condition of running a septic tank or treatment plant without a permit. You must:

• maintain the system regularly, following the manufacturer’s instructions;
• have maintenance done by someone competent;
• repair or replace it if it develops a fault, such as leaks, cracks, blockages, poor drainage or sewage smells;
• empty it before it reaches capacity, and at least once a year unless the manufacturer says otherwise;
• use a registered waste carrier to take the sludge away.

SEPA asks for the same in Scotland, including annual de-sludging and checks on soakaways and outfall pipes. Natural Resources Wales publishes a householder guide to running a system along the same lines.

A yearly maintenance plan

Every year: empty the tank

Book the tanker before the tank is full, not after. Ask the driver to check the inlet and outlet, the baffles or tees, and the condition of the walls while the tank is empty. Published UK guides put emptying at about £120 to £350 a visit, depending on tank size and access.

Check the firm is a registered waste carrier on the public register, and keep the receipt.

Every few months: walk the drainage field

Look for:

• grass noticeably greener or lusher over the trenches;
• soft, wet or sunken ground;
• standing water or effluent on the surface;
• sewage smells near the field or the tank.

Any of these means the field is struggling. Catching it early can mean a repair rather than a new field.

All the time: watch what goes in

The bacteria in a septic tank do the work. Anything that kills them or that they cannot break down shortens the life of the system.

Normal household cleaning is fine in normal amounts. It is the bucket of bleach after a party that does the damage.

Treatment plants need more

A sewage treatment plant has a blower or compressor, sometimes a pump and an alarm. On top of yearly emptying it needs a service, usually once a year, by an engineer who knows the make. One maker puts total running costs for a plant, including power, servicing and emptying, at about £350 to £800 a year. If the alarm sounds, deal with it promptly: a stopped blower means the plant is acting as a poor septic tank.

Keep a record

Keep a folder with:

• the make, model and size of the tank or plant, and when it was installed;
• a plan showing where the tank and drainage field are;
• every emptying receipt and service sheet;
• any repairs or changes.

In England, when you sell, the rules require you to give the new owner written details of the system and its maintenance. A buyer’s surveyor will ask for this anyway, and a tidy file makes the sale smoother.

Things that do not help

Septic tank additives, starters and “enzyme” treatments are widely sold. A working tank gets all the bacteria it needs from normal household use, and none of the regulators lists additives as part of maintenance. They are no substitute for emptying: no product removes the sludge that builds up in the bottom of the tank. Nor is pumping the tank out every few weeks a good idea unless it is a cesspit; a septic tank needs to keep some working liquid and bacteria to do its job.

When maintenance is not enough

If the field stays wet after emptying, smells persist or the tank is cracked, maintenance has run its course. The usual next steps are a new drainage field, a replacement tank, or a switch to a treatment plant. If your tank drains to a stream or ditch in England or Wales, it has to be dealt with regardless of its condition: see the septic tank regulations.

Signs to call someone now

• Sewage backing up into the house.
• Effluent on the surface of the garden.
• A strong, constant smell.
• The tank filling much faster than usual.

If any of those sound familiar, ask an installer to look at it. The form below finds one who works in your area.