Glossary of Drainage Terms
Confused by the jargon in your CCTV drainage survey report? Use our comprehensive A-Z guide to understand exactly what your drainage engineer is talking about.
Aco Drain
A popular brand name often used generically to describe channel drainage or trench drains used to manage surface water.
Benching
The sloping concrete floor of a manhole or inspection chamber, designed to direct the flow of wastewater into the main channel and prevent solid waste from accumulating.
CCTV Drainage Survey
A detailed inspection of an underground drainage system using a specialized, waterproof camera. Used to identify blockages, leaks, structural damage, and root ingress without excavation.
Combined Sewer
A single sewer pipe that is designed to carry both foul water (sewage) and surface water (rainwater) to a treatment plant.
Culvert
A tunnel or structure that allows water to flow under a road, railroad, trail, or similar obstruction.
Descaling
The process of removing scale, rust, concrete, and other hard deposits from the inside of a drainage pipe, typically using specialist mechanical tools or high-pressure water jetting.
Effluent
Liquid waste or sewage discharged into a river, the sea, or a drainage network.
Fatberg
A extremely large mass of solid waste in a sewerage system, consisting primarily of congealed fat, oil, grease (FOG), and non-biodegradable items like wet wipes.
Foul Drainage
The system of pipes that carries wastewater away from toilets, sinks, baths, showers, and household appliances to the sewer or septic tank.
Gully
A drainage fitting designed to collect surface water from outside areas or domestic wastewater from kitchens and bathrooms, incorporating a trap to prevent foul odors from escaping.
High-Pressure Water Jetting
A highly effective method of cleaning drains and sewers using water propelled at high speeds to break down blockages, cut through roots, and flush out debris.
Interceptor
A trap (often a Buchan trap) historically fitted to a drain near the property boundary to prevent foul air and rodents from the main public sewer from entering the private drainage system.
Invert Level
The level of the lowest point of the inside of a pipe or channel. Crucial for calculating the gradient or 'fall' of a drainage system.
Manhole / Inspection Chamber
An opening with a removable cover that provides access to an underground sewer or drain for inspection, maintenance, and unblocking.
Pitch Fibre
A type of pipe made from wood cellulose impregnated with coal tar, widely used in the UK from the 1950s to the 1970s. Known for blistering, delaminating, and collapsing over time.
Rodding
A traditional method of clearing blockages by pushing flexible, interlocking rods through the drainage system.
Root Ingress
When tree or plant roots penetrate and grow inside drainage pipes, usually entering through cracked pipes or displaced joints, causing severe blockages and structural damage.
Soakaway
A buried pit, typically filled with rubble or plastic crates, into which surface water is piped so that it can slowly percolate out into the surrounding soil.
Soil Vent Pipe (SVP)
A vertical pipe that carries soil and wastewater from upper floors to the underground drainage system, while also venting sewer gases safely to the atmosphere above the roofline.
Subsidence
The gradual caving in or sinking of an area of land. In the context of drainage, it is often caused by leaking drains washing away the subsoil supporting a building's foundations.
Surface Water
Rainwater that runs off roofs, driveways, patios, and other hard surfaces. This should ideally be directed to a soakaway or a dedicated surface water sewer, not a foul sewer.
Trap
A U, S, or J-shaped section of pipe that retains a small amount of water to create a seal, preventing foul sewer gases from entering a building.
WRC (Water Research Centre)
An independent organization that provides the standard classification and coding system for drain and sewer defects used in professional CCTV drainage survey reports.
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