How to Manage Your Off-Mains Sewage System

If you live in rural Hampshire, you may be more aware of where your waste goes than most people. Instead of being connected to the main sewer network, you may rely on a private 'off-mains' system like a cesspit, septic tank, or sewage treatment plant. But did you know that issues with these systems can damage your home, harm the environment, and even land you in legal trouble?

There are many ways that faults can occur, from tree roots and ground movement to more preventable causes. A 2015 Natural England report found that many septic tanks, for example, are improperly sized, sited, or maintained. In some cases, the phosphorus concentration of nearby streams rose by 700%, with terrible consequences for wildlife.

Luckily, this situation is avoidable with a little care and know-how. If you have an off-mains system, you must follow certain rules by law or risk enforcement action from your Local Authority or the Environment Agency. That aside, good management will improve your system's efficiency and reduce the risk of expensive faults. Let's look at how to keep your system safe, legal, and effective.

Legal responsibilities

If your home uses an off-mains sewage system, you must follow some ‘general binding rules’ or risk enforcement action. These can be complex, but here are our top tips:

Use the right system - your system and drainage field must be suitable for your use, and meet the relevant British Standard for when they were installed.
Manage your discharges - depending on your system’s location and the volume of its discharges, you may need a permit. The discharges must not cause pollution.
Empty your system regularly - how often will depend on its type, its size, and the number of people using it. Seek guidance from a specialist company.
Maintain your system regularly - the manufacturer or a specialist company can suggest a maintenance schedule. Any faults must be repaired immediately.
Notify new owners - if you sell your home, you must inform the buyer about your system in writing and provide maintenance records if possible.

It’s important to understand your legal responsibilities, so we recommend checking the full details on the Environment Agency's webpages.

What not to flush

Your off-mains drainage system receives everything that goes down your toilets, sinks, and showers. These systems are designed to handle soft or liquid organic waste, and the wrong additions can make them inefficient or cause them to fail entirely.

Some items can easily cause blockages in your system, so pop these in the bin instead:

Fat, oil, and grease
Food waste
Cat litter
Cotton buds
Nappies and sanitary towels
Wipes (even ‘flushable’ ones)

Other items kill the bacteria that are crucial for breaking down waste inside your system. Dispose of these at an appropriate place:

Medicines - local pharmacy
Disinfectants, and antibacterial products - suitable recycling centre
Houseplant and garden pesticides - suitable recycling centre
Bleach, caustic soda, and drain cleaner - suitable recycling centre

While it may sound odd, you should also watch your water input: if a large amount enters your system in a short period of time, it can flush out waste that should remain in the tank. Ensure no gutters or gullies are connected to your system, and spread out your use of dishwashers and washing machines.

Signs of trouble

Getting to know your system, and keeping a watchful eye on it, are crucial to reducing the risk of problems. You'll be better able to spot any faults and deal with them before them escalate. Look out for:

Gurgling pipes or sinks, showers, and toilets draining slowly.
Foul smells either inside or outside your home.
Swampy ground or pooling water near your system.
Areas of lush grass growth near your system.
Water or waste leaking from the tank lid or manhole covers.
Dark, thick, or smelly waste coming from the discharge pipe.
A grey, fluffy film on the ground (a.k.a. 'sewage fungus').

If in doubt, seek advice from a specialist drainage company. Remember: tackling potential problems early on can help you avoid property damage, environmental fines, and larger repair bills later on.

Keep our chalk streams clean

How best to deal with waste is a complex problem, and one that will only get more complex as our population expands. With new people and properties putting pressure on nature, off-mains users have a crucial role to play in shaping its future. This is especially true of our local chalk streams – some of our most precious and vulnerable ecological gems.

There are several ways that you can help, the most important being to manage your system effectively. You could also spread the word to your neighbours, encouraging them to do the same. We're seeking passionate people to raise awareness about this issue through the Septic Smart project, and can support you with training and information resources - get in touch to learn more.

Explore the Septic Smart project

How off-mains sewage systems work

How off-mains sewage systems impact the environment