Q&A: septic tanks

John Conlin / 27 November 2018

Chartered surveyor John Conlin answers reader questions on septic tanks.

Question: Do we need to replace our septic tank?

The firm that empties our septic tank tells me that I need to replace it with a ‘treatment plant’ within two years to comply with new rules about private sewage disposal.

Is this true or clever marketing?


New rules do come into force in 2020 but only apply to septic tanks that discharge the effluent into ditches, streams, rivers or lakes and coastal waters.

The intention is to reduce contamination as treatment plants purify the liquid sewage to a much higher standard. Septic tanks that discharge the liquid sewage direct into the ground via a soakaway are exempt from the new rules.

Question: can a septic tank just stop working?

We are not on mains drainage and share a septic tank with two adjoining houses, over the past three years the tank has needed increasingly frequent emptying.

One of our neighbours thinks the tank has stopped working and has got a costly estimate for replacement. Do septic tanks just stop working and can they be repaired?


Apart from leaking there is very little that can go wrong with the tank itself. Mostly the problem is either misuse or a clogged outflow. The break down of solids and grease in the tank is done by bacteria and pouring bleach, bio-detergents, strong loo cleaners or anti-biotics down the drains will stop this bacterial process. This can be restored by dosing the tank with a septic tank additive. If the tank fills rapidly with liquid rather than solid sludge the problem is likely to be a blocked or exhausted soakaway and pressure jetting or replacement of the pipes may solve the problem.

The opinions expressed are those of the author and are not held by Saga unless specifically stated.

The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.