What Kind of Off-Mains Drainage System Do I Have?

If you occupy a property with an off-mains drainage system that you did not personally have installed, you may not be aware of exactly how that system works. There are multiple different types of off-mains drainage system that your property might have, and each of them needs to be maintained in a different way.

It can be difficult to know how your property’s drainage system is set up, because by their nature these appliances are hidden away underground, and householders will not be able to identify which is which simply by inspecting the above-ground infrastructure. However, it is important to find this out in order to make sure your drainage system can continue to function properly.

Here, we will explore the different types of off-mains drainage systems, and highlight the ways in which householders and homeowners can tell which system they have on their property.

What are the different types of off-mains drainage systems?

Off-mains drainage systems are utilised by properties that cannot be connected to the main sewer network. They are most commonly installed on remote or rural premises that are not located close to the main sewers, and ensure that wastewater and sewage generated by the property can be safely stored, processed and disposed of.

There are three common types of off-mains drainage system that are used by these properties:

Septic tanks – these are the most common type of off-mains drainage system, consisting of a large underground tank that separates the waste into layers, and discharges wastewater into a drainage field or soakaway system
Sewage treatment plants – these function similarly to septic tanks, but utilise mechanical components to treat and purify the waste, allowing the effluent to be discharged directly into a local watercourse
Cesspits – also known as cesspools, these tanks simply collect and store a property’s wastewater and sewage with no processing or treatment involved, meaning they need to be emptied more regularly.

How can I identify my off-mains drainage system?

All three of these types of off-mains drainage systems have their own unique maintenance and upkeep requirements, so it is essential that you know what kind of system you have and how to look after it properly.

Here are the easiest ways of identifying which type of system is in place on your property:

Septic tanks

Your property will have between two and four manhole covers on site, located in close proximity to each other
You will be able to see above-ground vent pipes, used to remove the fumes and gases from the tank and distribute them into the air
The tank will be connected to a drainage field or soakaway to discharge effluent
The equipment will usually need to be emptied out around once a year
To find out more about how to maintain your septic tank, take a look at our complete guide.

Sewage treatment plants

You will be able to see an electrical box mounted above ground, somewhere in the vicinity of the equipment
You may be able to hear a humming sound coming from the electrical supply
The tank may be equipped with an alarm system to alert you to potential problems
The treatment plant has a cover that is slightly raised above ground
The tank will need to be emptied out around once a year
Sewage treatment plant maintenance is largely similar to septic tank upkeep, but with the additional requirement to keep its electrical and mechanical components serviced each year as well.


Cesspits have only one manhole cover above ground
These tanks tend to fill up very quickly and require regular emptying
Keeping on top of cesspit maintenance is absolutely essential to avoid overflows or damage to the system. To learn more, take a look at our cesspit maintenance page.

Find out more

By following this advice and obtaining the right information from the seller, you will be able to get a clearer idea of what kind of off-mains drainage system your property uses, helping you keep the system properly maintained and protecting you against the potential risk of overflows, blockages and breakdowns.

If you are having a problem with your off-mains drainage system and want to ask for help from qualified drainage experts, give Lanes a call today. You can contact us 24/7 on 0800 526 488, or fill in our online enquiry form to request a call back at your convenience.

Lanes can help

If you're interested to know how Lanes can help you, get in touch with our team below.

Get in touch

Popular searches

Urgent help required?

Call our 24 hour helpline

0800 526 488