Maintaining a Septic Tank or Cesspit Properly

Know Your System: Septic Tank or Cesspit?

If your rural home isn't connected to mains drainage, you'll be relying on either a septic tank or a cesspit. They might look similar from the outside, but they work in very different ways. A septic tank is a treatment system: wastewater flows in, solids settle to the bottom as sludge, lighter fats and oils float to the top as scum, and the partially treated liquid flows out to a soakaway or drainage field. A cesspit is simply a sealed holding tank with no outlet — everything that goes in stays there until it's pumped out.

Why does this matter? Because maintenance differs. A well-sized septic tank for a typical three-bedroom home usually needs emptying once a year, though heavy water use or a small tank may mean every six to nine months. A cesspit fills much faster — often every four to eight weeks for a family — and requires more frequent emptying. If you're not sure which you have, check your property deeds, ask a neighbour, or look for two inspection chambers (septic) versus a single sealed lid (cesspit).

Why Regular Emptying Matters

Putting off an empty is a false economy. When sludge builds up, it reduces the working volume of your tank, so solids can escape into the soakaway. That clogs the drainage field, which is expensive to repair or replace. A neglected cesspit will back up into your home, causing unpleasant smells and potential health hazards. Regular emptying also gives your engineer a chance to spot cracks, faulty baffles, or high water levels that suggest a blockage.

Use a registered waste carrier — ask to see their licence. They should provide a waste transfer note. In England and Wales, you have a legal duty of care for your waste. In Scotland, check with SEPA; in Northern Ireland, the NIEA. Never use an unlicensed cowboy who offers to dump waste illegally. It's not just unethical; you could be liable for prosecution.

• Septic tank: empty when sludge and scum take up more than 30% of the tank's depth. A dipstick check before each annual service is wise.
• Cesspit: empty when the level reaches about three-quarters full. Fit an alarm or use a dipstick weekly if you have a large household.
• Best time: late summer or early autumn, before the ground gets too wet for heavy tankers.

What to Put Down the Drains — and What to Avoid

Your septic tank relies on bacteria to break down waste. Harsh chemicals kill those bacteria, turning your tank into a smelly, inefficient holding tank. The same goes for cesspits: nothing should go in that you don't want to store and pay to remove.

Safe: human waste, toilet paper (choose recycled, unbleached brands that break down quickly), mild washing-up liquid, soap, shampoo, and laundry detergent in moderation. Use phosphate-free and bleach-free products where possible.

Avoid: wet wipes (even "flushable" ones — they don't break down fast enough), sanitary products, nappies, cotton buds, condoms, dental floss, cooking fat, oil, grease, coffee grounds, eggshells, cat litter, and anything labelled "antibacterial" or "bleach". Also avoid heavy-duty drain cleaners; a mechanical plunger or enzyme-based treatment is safer.

• Fats and oils: pour into a container and bin them. A fatberg in a septic tank is a nightmare to clear.
• Medicines: return to a pharmacy. They disrupt the bacteria and can pollute groundwater.
• Greywater from a washing machine: try to spread loads across the week rather than doing five loads on a Sunday. A surge of water stirs up solids.

Looking After the Soakaway

If you have a septic tank, the soakaway (or drainage field) is where the liquid effluent is further treated by soil bacteria. It's a living system, so protect it. Never drive or park vehicles over it — the pipes can crush. Keep trees and deep-rooted shrubs at least 10 metres away; roots seek out moisture and will block the perforated pipes. Don't build sheds, patios, or extension footings over it either.

Check that surface water (roof downpipes, drive runoff) isn't directed into the soakaway. Extra rainwater overloads the system and can cause effluent to pond on the surface. If you notice soggy patches, bright green grass in dry weather, or a sewage smell outside, the soakaway may be failing. That's a job for a qualified engineer — not a DIY fix.

Warning Signs You Shouldn't Ignore

Septic tanks and cesspits rarely fail without warning. Catch problems early and you'll save money and stress. Watch for:

• Slow drains throughout the house, not just one fixture. That points to a full tank or a blocked outlet.
• Gurgling sounds after flushing or running a tap. Air is being sucked through the system because it's backing up.
• Unpleasant odours inside or near the tank. A healthy septic tank should have little smell.
• Standing water around the tank lid or soakaway. The ground should absorb liquid, not pool it.
• Dark, lush grass over the drainage field in summer. It often means effluent is rising to the surface.
• Backflow into the house — the most urgent sign. Stop using water immediately and call for an emergency empty.

If you see any of these, don't pour more water down the drains. Turn off the mains supply if you can, and call your local family-run plumbing and heating team. We've seen it all — and we'd rather fix a small issue than a flooded garden.