The sewers
Sewer pipes are normally made from clay or concrete and vary greatly in size. They are pipes that take the drainage of more than one property.
Sewers serving housing estates are usually between 150mm (six inches) and 225mm (nine inches) in diameter. In bigger towns and cities the sewers are big enough to walk through, up to 3.5 metres (11.5 feet) in diameter.
Modern homes generally drain into what is known as a separate system. In this case there are two sewers - one is a foul sewer which takes the sewage from washing machines, sinks and lavatories.
The second sewer takes surface water or rainwater which drains off roofs and driveways.
Older properties may be connected to a combined system in which one sewer takes both the sewage and surface water and transports it to a treatment works.