What Type of Off-Mains Drainage System Do I Have? - Proseptic

How do I know what type of off-mains drainage system I have?

septic tanks

Aside from your natural curiosity, you need to know what type of off-mains drainage system you have for maintenance reasons.

Depending on which kind your property uses, the servicing schedule and methods are very different.

Types of off-mains drainage system

Septic tanks

The most commonly used, based on a simple storage system with a pipe from your property to the tank.

Here the waste is separated, with wastewater discharged to a soakaway, drainage field or watercourse.

If your property has a septic tank, it’s likely you’ll have more than one above ground manholes in close proximity to each other.

Less likely (but possible), your system may incorporate vent pipes above ground. These discharge gases and unpleasant odours directly into the air.

If you do indeed have a septic tank, remember that it will likely need emptying once a year.

Sewage treatment plant

Offering a more sophisticated level of waste treatment, sewage treatment plants are increasingly preferred.

Due to the superior cleanliness of the waste processed, sewage treatment plants can discharge directly into the watercourse, unlike septic tanks.

Typically, the mechanical components used in a sewage treatment plant require an electricity supply.

So there will usually be an external power box mounted somewhere near the area (you may even hear a slight humming).

The cover for the sewage treatment plant will probably be raised slightly above ground.

When it comes to emptying, the same annual schedule as a regular septic tank should apply.

But in addition, your sewage treatment plant will also need servicing once a year to ensure continued correct functioning of components.


Cesspits are less common. They only really exist in situ where no electricity supply or traditional septic tank systems can be used.

Basically just a holding tank for your property’s waste, they need emptying much more frequently.

If there is only one above ground manhole at your property and no sign of an electrical supply, you may have a cesspit.

It may have been the case that legislation at the time of installation prevented a more suitable system being put in place.

But as the requirements for systems are regularly updated, it’s worth looking into whether you can replace it with a more efficient type.

Still not sure which off-mains drainage system is yours?

If you’re still unsure which type of off mains drainage system is at your property, you may need a survey.

If you’d like to talk to someone about arranging a convenient time for yours, please get in touch today.

Next Blog Post

What is a septic tank baffle?

A septic tank or small sewage treatment plant is an efficient system comprising of several different parts serving different functions. Some are self-explanatory (tank, reservoir, pipes) but if you’ve ever been, well, ‘baffled’ by what a septic tank baffle is, wonder no more. This unassuming but vital component is found at the junction between the [...]