Off mains drainage - a beginners guide!

Off mains beginners guide, How a septic tank works | By Sam Warren

Many people dream of a move to the country - rolling hills, tweeting birds and quaint cottages with thatched roofs. I mean, what's not to love? All that fresh air, no rush hour traffic and taking the dog for long walks through the fields. But that's not all that's different when compared to town and city life. If you own a property in the countryside, or you're looking to buy one, you might need to get to grips with the world of off mains drainage. Here's our beginners guide to the basics you need to know!

What is off mains drainage?

Approximately 95% of properties in the UK are connected to a main sewer. Waste from your property's toilets, sinks, showers and kitchen appliances will run through a network of pipes from your property until they meet with a main sewer, typically under a nearby main road. Your local Water and Sewage company will be responsible for the pipe work that runs from the boundary of your property, and if anything goes wrong with it, it's up to them to deal with it.

If your property is in a more rural location, it's likely that you will have off mains drainage. Put simply, this means that you will have a self contained drainage system which will take the waste from your property. It will usually be connected just to your property, but occasionally the system might be shared with other neighbouring properties.

What types of off mains drainage are there?

Your property's waste will flow from your property to some sort of tank. These are the three different types of tanks:

  • Septic tanks
Off mains drainage - septic tanks

A septic tank can come in all different shapes and sizes, as they have been in existence for a long time. They are the most common type of off mains drainage tank. Some are brick built, some are made of concrete, and more modern ones are made of glass reinforced plastic.

The basics of a septic tank is that it doesn't have any mechanical parts, and doesn't perform any `treatment' of the waste. The waste enters the tank, then separates into three different layers as above. The middle layer of separated waste water then leaves the tank, typically into a soakaway system. A soakaway system is a network of slotted or perforated pipes, which allow the waste water to percolate through the sub soils without causing a pollution. The remaining contents of the tank are then removed at regular intervals by a tank emptying company.

Please note - if you have a septic tank which discharges the waste water into a watercourse or ditch, this is no longer allowed. In fact, legislation coming into force in 2020 means that your system would need to be upgraded or replaced by 2020, even if it is not currently causing a pollution. You can download our guide to off mains drainage regulations here - we have tried to make this complicated subject matter as easy to understand as possible!

  • Cesspits
Off mains drainage - cesspit

A cesspit is literally just a holding tank for the waste from your property. Waste goes in and stays there until the tank is emptied. There is no treatment of the waste that goes in, it simply separates into three layers within the tank. Cesspits are not very common for a couple of reasons - firstly because they pose a greater threat to the environment if they fail, but also because they require a lot of emptying which can become expensive for the property owner.

  • Sewage treatment plants
Off mains drainage tank - sewage treatment plant

A sewage treatment plant is the most modern form of off mains drainage tank. Powered by an electricity supply, a sewage treatment plant provides treatment of the waste, which means that the waste water that leaves it is cleaner than that which would come from a septic tank. This in turn means that the waste water from a sewage treatment plant can go straight to a watercourse or ditch.

How expensive is off mains drainage?

The good news is that you won't have to pay sewerage rates once you own a property that has off mains drainage. This can vary but is typically around £400-£500 per year. But before you start planning what to spend it on, the flip side is that you will need to pay to have your tank emptied (also known as being `desludged' but that term is not very pleasant so we'll stick with emptied for now). As a general rule of thumb, most septic tanks and sewage treatment plans need to be emptied annually. There are huge regional variations in prices for tank emptying, but most prices are somewhere between £120-£250. If you have a cesspit, you'll be looking at needing to get the tank emptied between 4 and 8 times a year.

Sewage treatment plants also need regular servicing of the moving parts - this is usually done annually and usually costs around £150.

Is it expensive to repair or replace off mains drainage?

If you look after your off mains drainage system, you should get years of trouble free use from it. However, there are things that can happen to your drainage system that can cause it to become damaged. Amongst other things, ground pressure can cause tanks to crack, or tree roots can grow through the walls of the tank or the soakaway pipework.

It is often difficult to repair an off mains drainage system, depending on the damage that has been caused. And the bad news is that replacing a drainage system in its entirety typically costs upwards of £10,000. However, the better news is that if you have the right buildings insurance in place, you should have cover for the costs of sorting out any septic tank problems or soakaway problems. Here at UKDP, we specialise in managing insurance claims for damaged off mains drainage systems, and we can manage everything for you from start to finish. We can also help you to work out if you have the right cover in place already, check out our septic tank insurance page here, and also our article on the 5 things to consider when choosing the right buildings insurance policy.

I hope this has given you some useful basic information on the world of off mains drainage. If you want to know more (and who wouldn't, right?!) please browse through our other articles and videos in our Knowledge Hub section. If you can't find what you're looking for there, just give our friendly team a call on 0800 028 9903 or contact us here.

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