What is a Cesspit NZ?

A cesspit or catchpit is a drainage system used primarily in stormwater management. Whether it is sewerage or stormwater, a cesspit is designed to prevent blockages and water contamination in a drainage system. A cesspit is a camber that allows debris and sediments to settle to the bottom of a pit. For this reason it is advisable to regularly maintain your cesspit by emptying and cleaning at least once a year.

Why do you need a cesspit?

A cesspit is typically found upstream of a drainage system. This way the cesspit can collect all debris before it enters public or private stormwater pipes.

Cesspits are most commonly found in gardens, driveways or roadways. These environments typically collect large quantities of debris and sediment which if allowed through would cause blockages in a public drainage system. A blockage could cause flooding, water to return back up a pipe or worse damage property. Therefore a cesspit is vital when managing surface water in any of these environments.

By law all channels and subsoil drainage must flow into a cesspit to ensure no debris can flow into the private or public stormwater lines. For example, a driveway channel may be a vector for debris to collect, and so all water must be filtered before it can be discharged into the stormwater line.

How does a cesspit / catchpit work

Basically, a cesspit works by providing a sump where sediment and debris can fall and collect. Water overflows at the top level of the cesspit leaving debris behind at the bottom of the pit. The clean water then exits through the outlet pipe, which sits just lower than the inlet pipe.

To protect the outlet pipe against potential floating debris, a baffle can be fitted to the outlet. This can help filter leaves and twigs, stopping them from entering the pipe.

Because silt, sediment and debris build up in the sump of the cesspit, regular maintenance and cleaning of the cesspit is required. Typically the average cesspit should be cleared out annually to prevent a build up of debris. Such a build up could cause the cesspit to become ineffective, increasing the likelihood of damage from unmanageable water.

Types of cesspits

The most common form of catchpit is a roadside catchpit. Catchpits can be found intermittently alongside Auckland roads. What is unique about these types of catchpits is their design. Roadside cesspit openings must not allow objects greater than 100mm in dimension to pass through. Openings must also be small enough to prevent sizable debris from entering the system that may cause damage. These cesspits are typically larger than ones found on residential property. Under New Zealand building code these cesspits are known as a type 2 surface water sump.

A type 1 cesspit is no larger than an office paper bin. These cesspits are commonly used in residential applications such as in a driveway or garden.

There are many different names for a cesspit, such as:

  • Catchpit
  • Bubble up chamber
  • Receiving chambers
  • wet chambers
  • Dry chambers

Regardless of the name, the principles are the same. Incoming water is filtered to remove contaminants before entering a larger drainage system. This now clean water can then be confidently reused, recycled, or safely discharged into our oceans or environment.

Cesspits come in a variety of materials. The physical sump is typically made of:

  • Concrete
  • Polyethylene plastic

The top grate of a cesspit is typically made of iron. Iron grates are extremely durable and heavy. This prevents the grate from blowing away in strong weather.

With the increasing popularity of bicycle lanes, a newly designed cesspit finish is becoming more common. This new design is a flat stainless steel grate. Unlike the normal curved iron grate, this cesspit finish is designed to prevent accidents on bikes and scooters. More traditional curved grates can act like a pothole, dismounting commuters off their bike.

Maintenance

Because a cesspit is a static installation designed to filter stormwater it can quickly become full. If Debris and sediment pile up it will cause a blockage, damage and even flooding. Therefore it is necessary to regularly maintain cesspits by clearing excess waste. Ideally this should be done yearly.

Every homeowner should be concerned whether their cesspit is functional or not. One quick test you can do at home is to look down into your cesspit. If you cannot see an outlet pipe then it most likely means your cesspit is overflowing or blocked.

We at Drainage NZ offer our own regular maintenance service. Book with us and receive annual maintenance on your cesspit. We’ll turn up at the same time every year to empty and clean your cesspit with no fuss and at a competitive price.

Give us a call on 0800 372 465 or contact us online to organise maintenance on your cesspit.