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Ask the experts

Robert Hamilton


How to maintain a septic tank

Searches show that the cottage I am buying has a septic tank and I confess I am worried enough to consider withdrawing my offer – should I be concerned? Few things gladden the heart of this surveyor more than an easy-to-open manhole cover revealing shiny, ceramic drains flowing freely beneath. More often in the Cotswolds, heavily corroded covers with broken handles create a shower of rust as they are finally levered open, also giving me back pain and trapped fingers, but this is a good sign because clearly the drains haven’t caused a problem for years. Similarly, your septic tank is unlikely to be a worry if you abide by a few simple guidelines. The Cotswolds’ interesting drain infrastructure relates to the old age of many properties. In newer properties, rainwater from roofs and road surfaces is directed into rivers and only foul / wastewater (from baths, washing machines and so on) drains into the sewage system. In older properties, combined drains direct everything to the treatment works – in fact, this was one of the problems of flooding in recent years, when overloaded drains caused sewage discharge. Either way, in a treatment works the wastewater is screened for grit and solids before being allowed to settle.The heavy sludge at the bottom is taken off for further treatment whilst microorganisms work to clarify the remaining wastewater before the cleaned water is returned to rivers and eventually out to sea. Your septic tank acts just like a mini treatment plant.There are many varieties from old brick-built two-chamber types allowing wastewater to ‘soak-away’ via crushed stone and gravel to modern tanks (from sophisticated manufacturers such as Klargester) where decomposition is aided by air pumped through the system - these are really mini-sewage plants suitable even for small housing developments. However, all types rely on friendly bacteria to function properly. In a septic tank, solids settle in the first chamber to be digested and mineralised by bacteria whilst liquid flows to the second

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and third chambers, each time settling until the effluent flows out into the ‘drainage field’ or soak-away and only requiring an annual ‘pump out’ to remove the settled matter. It should not smell nor pool with water round about. Constant foul odour or slow / backing-up drains are telltale signs that your tank needs pumping. One should limit the volume of water travelling through, which you can do by using ‘Hippos’ in WC cisterns and ensuring that rainwater is diverted into a separate harvesting system, but bacteria regeneration kits are not necessary providing the tank is well maintained and in regular use. A domestic salt-operated water softener, on the other hand, will benefit the system as well as your pipework and sanitary goods. The golden rules of sensible maintenance apply to mains drainage as well as a septic tank. 1. Use ‘eco’ detergents and soaps. 2. Don’t dispose of chemicals or wash paintbrushes in the sink and don’t tip away cooking fat / coffee grounds down the drain, either. 3. Most importantly don’t flush wipes, dental floss, nappies or sanitary products down the loo - wrap, bag and bin anything other than toilet paper, as “biodegradable” products will still clog drains and/or take years to break down. If you are sensible with maintenance, your septic tank will be very efficient - it will function almost effortlessly for many years and certainly is not a valid reason to withdraw from your property purchase. Central Surveying has offices in the Cotswolds and Knightsbridge, specialising in independent professional surveying and property consultancy services for commercial and residential clients in the Cotswolds, South West and London. Robert Hamilton works from Naunton in the heart of the North Cotswolds.To contact Robert, telephone 01285 640 840 or visit

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