If your property is not connected to mains sewage drains, which is very common in remote and rural location, you'll most likely have or require a either a cesspool, septic tank or sewage treatment plant. This has no connection to the public sewerage system and is known as off-mains drainage.
Basically there are 3 types of tank offering different levels of treatment.
1. A simple holding tank, known as a cesspool. These have no sewage treatment and simply hold the waste to be removed by a vacuum tank before the tank fills. These are the least preferred option as they have high running costs and will require the largest tanks but do not require a soak-away or draining as 100% of the waste is kept within the tank.
2. A Septic Tank is designed to provide primary treatment to crude wastewater. It retains solids and allows them to settle out in a primary settlement chamber, where they can be partially broken down by biological action so that only the remaining liquor (normally called effluent) is then sufficiently treated to soak into the ground in an underground soak-away system, where the oxygen and bacteria in the earth will provide further biological treatment.
3. Sewage Treatment Plants are designed to treat the waste to a much cleaner level within the tank, where the output is up to 97% clean and allowed to drain to in a water course, stream or drainage ditch or a soak-away system. This is achieved by introducing more oxygen and/or mechanical devices to break down the waste to allow for fast biological decomposing to take place. For larger installation this process can be achieved with a system of several tanks each specifically designed to process the waste sewage using different methods.
Soak-away systems: If you have a sewage treatment plant with no access to open drainage or you have a septic tank you will require a well designed and installed soak away system to allow for the discharge from the tank to soak away into the ground for further biological treatment. Most problems with septic tanks and systems are caused by lack of maintenance or a soak away system that cannot cope with the required output.