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.
Attenuation Tank
A large underground storage tank designed to hold excess surface water during heavy rainfall, releasing it slowly into the drainage system to prevent flooding.
Backfall
A defect where a pipe slopes in the wrong direction (upwards instead of downwards), causing water and waste to pool rather than flow away.
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.
BOD (Biochemical Oxygen Demand)
A measure of the amount of oxygen required by aerobic microorganisms to decompose organic matter in water. Used to gauge the polluting strength of wastewater.
Build-Over Agreement
A legal agreement required by a water authority if you plan to build over or within 3 meters of a public sewer.
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.
Cesspit
A sealed underground tank that collects sewage and wastewater. Unlike a septic tank, it does not treat the waste or have an outlet, so it must be emptied regularly by a vacuum tanker.
Combined Sewer
A single sewer pipe that is designed to carry both foul water (sewage) and surface water (rainwater) to a treatment plant.
CON29DW
A standard drainage and water enquiry report used during property conveyancing to confirm if a property is connected to public sewers and mains water.
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.
Displaced Joint
A structural defect where two sections of pipe have moved out of alignment, creating a step or gap that can snag waste and allow water to leak out or roots to enter.
Dye Testing
A method used to trace the flow of water and confirm connectivity within a drainage network by adding a harmless, brightly colored dye to the water.
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.
Flail
A specialist attachment used with high-pressure water jetting or mechanical milling machines, featuring spinning chains or blades to cut through tough roots or hard scale.
FOG (Fat, Oil, and Grease)
A major cause of blockages in commercial kitchens and restaurants. FOG solidifies in pipes, leading to fatbergs.
Foul Drainage
The system of pipes that carries wastewater away from toilets, sinks, baths, showers, and household appliances to the sewer or septic tank.
French Drain
A trench filled with gravel or rock containing a perforated pipe that redirects surface water and groundwater away from an area.
Grease Trap / Grease Interceptor
A plumbing device designed to intercept most greases and solids before they enter a wastewater disposal system. Essential for commercial kitchens.
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.
Lining / Relining
A no-dig repair method where a resin-impregnated felt tube is inserted into a damaged pipe and cured in place, creating a new, seamless pipe within the old one.
Manhole / Inspection Chamber
An opening with a removable cover that provides access to an underground sewer or drain for inspection, maintenance, and unblocking.
Patch Repair
A localized no-dig repair used to fix a specific, isolated defect (like a single crack or displaced joint) rather than relining the entire pipe length.
Percolation Test
A test to determine the absorption rate of soil for a septic drain field or soakaway. Required for BRE365 compliant soakaway design.
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.
PPM (Planned Preventative Maintenance)
A scheduled program of drain cleaning and inspection designed to prevent blockages and emergencies before they occur. Common in commercial settings.
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.
Section 104 Agreement
A legal agreement under the Water Industry Act 1991 for a water authority to adopt a newly constructed private sewer, taking over responsibility for its maintenance.
Section 106 Agreement
A legal agreement granting permission to connect a private drain or sewer to a public sewer network.
Septic Tank
An underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater flows for basic treatment. Solids settle and liquids discharge to a soakaway.
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.
Sonde
A small radio transmitter that can be attached to a CCTV camera or drain rod. It emits a signal that is picked up by a receiver above ground, allowing engineers to pinpoint the exact location and depth of a pipe or defect.
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.
SuDS (Sustainable Drainage Systems)
Water management practices designed to align modern drainage systems with natural water processes, reducing surface water flooding and improving water quality.
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.
Vacuum Tanker
A specialized truck equipped with a large tank and a powerful vacuum system, used for emptying cesspits, septic tanks, grease traps, and flooded areas.
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.