Septic Tank vs. Cesspit: Understanding Your Off-Mains Drainage

If your property isn't connected to the main municipal sewer network—a common scenario in rural parts of Kent, Surrey, and Sussex—you likely have a septic tank or a cesspit. While they both handle wastewater, they operate in completely different ways. Knowing which one you have—and how it works—is crucial for your property's value, your legal responsibilities, and the health of the local environment.

The Septic Tank: The Mini-Treatment Plant

A septic tank is an active system that partially treats the waste. It usually consists of two chambers. In the first chamber, solid waste settles at the bottom (forming sludge), while fats and oils float to the top. In the middle, partially clarified water flows into the second chamber and then out into a 'soakaway' or drainage field. Here, the soil naturally filters out any remaining impurities before the water re-enters the groundwater.

Because a septic tank only holds the solid waste, it only needs emptying (desludging) once or twice a year, depending on the number of people in the house. This makes it a relatively low-maintenance option as long as you aren't flushing chemicals or grease that kill the natural bacteria in the tank.

The Cesspit: The Sealed Holding Tank

A cesspit (or cesspool) is a much simpler, but more demanding, system. It is essentially a large, sealed underground container with no outlet. Every single drop of water that goes down your sink, shower, or toilet stays in the tank. There is no treatment and no soakaway. Once the tank is full, a vacuum tanker must be called to empty it entirely.

Cesspits require much more frequent emptying, often every few weeks if a large family is using the system. They are usually only installed where the ground conditions are unsuitable for a soakaway (such as heavy clay soil) or where there are environmental restrictions near watercourses. They must be monitored closely to prevent overflows, which are a major pollution risk and can lead to heavy fines.

The 2020 General Binding Rules

The UK government introduced strict new regulations in 2020. Key among these is the requirement that septic tanks must no longer discharge directly into a watercourse (like a stream or river). If your system does this, it must be upgraded to a sewage treatment plant or replaced with a proper drainage field. At Call2Drain, we provide full health checks and compliance reports to ensure your off-mains system is legal and environmentally sound.

Maintenance Tips

Regardless of which system you have, you must be careful about what goes into it. Avoid using heavy bleach or anti-bacterial cleaners, as these kill the 'good' bacteria in a septic tank. Don't flush anything but toilet paper, and ensure that only wastewater (not rainwater from your roof) enters the system. Excess rainwater can overwhelm a septic tank, washing solids out into your soakaway and potentially ruining it. Regular tanker services from Call2Drain ensure your system remains in peak condition and avoids the mess of a backup.