UK Drainage Glossary

A drainage pipe obstructed by debris, grease, roots, or other materials preventing normal water flow. Symptoms include slow drainage, gurgling sounds, and foul odors. Most blockages occur within 3 meters of the property, with 70% caused by inappropriate items being flushed or poured down drains. Typical cost to clear: £80-£150.

A diagnostic inspection using waterproof cameras mounted on flexible rods inserted into drains to identify blockages, damage, root ingress, or structural issues. Cameras can navigate pipes 25-100mm diameter and record high-definition footage with distance markers. Essential for pre-purchase property surveys and diagnosing recurring problems. Typically costs £150-£300 and takes 1-2 hours.

An underground wastewater treatment system used in properties not connected to mains sewerage, typically in rural areas. Treats wastewater through bacterial decomposition in chambers, with treated effluent discharging to a drainage field or soakaway. UK septic tanks must comply with General Binding Rules since 2020, requiring emptying every 1-3 years depending on size and usage.

High-pressure water cleaning method (typically 3,000-4,000 PSI) used to clear blockages and remove scale, grease, and debris from drainage pipes. More effective than rodding for stubborn blockages and can cut through tree roots. Professional equipment delivers 20-40 liters per minute at high velocity, scouring pipe walls clean. Costs £150-£300.

An underground drainage system that disperses surface water (rainwater from roofs and driveways) into the surrounding soil through percolation. Typically constructed as a 1-3 cubic meter pit filled with clean rubble or plastic crates wrapped in geotextile membrane. Must be 5 meters from buildings and not in clay soil. Building Regulations Part H requires soakaways for most new builds where mains drainage isn't available.

An access point to underground drainage systems allowing inspection, cleaning, and repairs. Also called inspection chambers. Manholes are positioned at junctions, changes in direction, or every 22-45 meters along drain runs as required by Building Regulations. Modern chambers use plastic or pre-cast concrete with sealed covers.

Tree or plant roots penetrating drainage pipes through joints, cracks, or collar connections, seeking moisture and nutrients. Particularly common in Victorian properties with clay pipes and in areas with willow, poplar, or oak trees. Roots can grow 20-30 meters from the tree and exert pressure exceeding 2,000 PSI. CCTV surveys reveal roots in 40% of recurring blockages.

A no-dig repair method inserting a resin-coated liner into damaged pipes which is then inflated and cured to form a new pipe-within-a-pipe. Cured-in-place pipe (CIPP) technology eliminates excavation, typically completed in 1-2 days. Suitable for cracks, root damage, and deterioration. Adds 50+ years to pipe life. Costs £800-£2,000 vs £3,000-£6,000 for excavation.

A mass of congealed fat, oil, grease (FOG), and non-biodegradable items like wet wipes forming rock-hard blockages in sewers. Can grow to enormous sizes—the largest UK fatberg in Whitechapel weighed 130 tonnes. Costs UK water companies £100 million annually to remove. Prevented by never pouring grease down drains and only flushing the '3 Ps': pee, poo, and paper.

A device installed in drainage systems to capture sediment, oil, or grease before it enters the main sewer. Required in commercial kitchens, car washes, and industrial premises under Building Regulations and trade effluent consents. Works by separating lighter fats/oils which float, allowing cleaner water to pass through. Must be emptied regularly.

UK building regulations governing drainage and waste disposal in England and Wales. Sets standards for drain sizing, gradients (1:40 to 1:80 minimum), access points, separation of foul and surface water, ventilation, and testing. Any new drainage work or significant modifications require Building Control approval and inspection.

An outdoor drainage connection point with a grid or grate that collects surface water from yards, driveways, or downpipes. Contains a water trap to prevent sewer gases escaping. Common blockage points from leaves, silt, and debris. Should be cleaned quarterly by removing the grid and scooping out sediment.

Traditional method of clearing blockages using flexible rods screwed together and pushed through drains. Effective for simple blockages within 5-10 meters of access point. Less effective than jetting for stubborn blockages, grease, or scale buildup. Rods are rotated clockwise (never anticlockwise or they unscrew) with various attachments including plungers and scrapers.

Drainage pipes made from wood cellulose fibers impregnated with coal tar pitch, commonly installed 1950-1970s. Known to delaminate, collapse, and deform ('blistering') after 40-50 years, causing severe blockages. Identified during CCTV surveys by corrugated appearance and oval cross-section. Requires replacement, cannot be effectively repaired.

Traditional drainage pipes made from fired clay, used in UK drainage for over 150 years. Extremely durable and chemical-resistant but vulnerable at joints where roots can penetrate. Victorian properties almost exclusively used clay pipes. Can last 100+ years but joint failure and root ingress are common issues.

Modern plastic drainage pipes made from unplasticised polyvinyl chloride. Lightweight, easy to install, chemical-resistant, and with smooth internal surfaces reducing blockage risk. Standard for new UK drainage installations since the 1980s. Available in orange (underground) and grey (above ground) with push-fit or solvent-weld joints.

Also called a leach field or soakaway field. A system of perforated pipes laid in gravel-filled trenches that disperses treated effluent from septic tanks or treatment plants into the soil. Must be designed according to percolation test results and be 50m from water sources. Requires periodic maintenance and typically lasts 20-30 years.

A package sewage treatment plant that actively treats wastewater using mechanical aeration and biological processes, producing cleaner effluent than a septic tank (95% vs 40% treatment). Can discharge directly to watercourses with Environment Agency permit. Requires electricity and annual servicing. Installation costs £4,000-£10,000.

A sealed underground tank that collects wastewater without any treatment or discharge. All contents must be removed by tanker, typically every 4-6 weeks for a family of 4. The most expensive and environmentally poor option. Being phased out—new cesspits rarely permitted. Annual emptying costs can exceed £3,000.

A soil test measuring how quickly water drains through the ground, required before installing a drainage field or soakaway. Involves digging trial pits, filling with water, and timing the drop. Results expressed in seconds per millimetre (s/mm). A Vp of 12-100 s/mm is suitable for drainage fields. Tests cost £200-£400.

Environment Agency regulations introduced January 2020 governing septic tanks and small treatment plants in England. Key requirements: no direct discharge to watercourses from septic tanks, regular maintenance, use of registered waste carriers for emptying, and upgrading non-compliant systems when selling property. Similar rules apply in Wales and Scotland.

Written consent required from your water company before building over or within 3 meters of a public sewer. Protects the sewer and ensures future access for maintenance. May require CCTV survey before and after construction. Failure to obtain can affect property sale and cause enforcement action.

Contaminated wastewater from toilets, sinks, baths, showers, washing machines, and dishwashers. Must drain to mains sewers or septic tanks/treatment plants for proper treatment. Building Regulations require complete separation from surface water drainage. Also called sewage or black water.

Clean rainwater collected from roofs, driveways, patios, and hard landscaping. Should drain to soakaways, storm drains, or watercourses—never to foul sewers. Many UK properties have separate surface water drainage systems. Connecting surface water to foul sewers is illegal and causes sewer flooding.

An older type of sewer system that carries both foul water and surface water in a single pipe. Common in Victorian-era urban areas. During heavy rainfall, these systems can become overwhelmed, leading to combined sewer overflows (CSOs) discharging untreated sewage to rivers. Being gradually separated by water companies.

A sewer within your property boundary that serves only your property. You are responsible for its maintenance and repair. Since the Private Sewers Transfer 2011, most shared sewers and lateral drains became public (water company) responsibility. Check with your water company if unsure.

The section of drain running from your property boundary to the main public sewer. Since October 2011, most lateral drains transferred to water company ownership under the Private Sewers Transfer. If your lateral drain was built before July 2011, it's likely now the water company's responsibility.

A small access point in drainage systems specifically designed for inserting drain rods, typically with a screwed cap at ground level. Positioned where manholes would be impractical, such as under buildings or in tight spaces. Allows blockage clearing without full inspection chamber access.

Also called a Durgo valve. A mechanical device that allows air into drainage systems to prevent trap siphonage without requiring an external soil vent pipe. Opens under negative pressure to admit air, closes to prevent odors escaping. Commonly used in loft conversions and extensions where external venting is impractical.

A covered access point in drainage systems allowing visual inspection and maintenance of pipes. Shallower than manholes (typically under 600mm deep). Located at junctions, direction changes, and gradient changes as required by Building Regulations. Modern versions use plastic with sealed covers.

The slope or fall of a drainage pipe, expressed as a ratio (e.g., 1:40 means 1mm fall per 40mm run). Building Regulations Part H specifies minimum gradients: 1:40 for 100mm pipes with 1 WC, 1:80 for 100mm pipes with 5+ WCs. Correct gradient ensures self-cleansing velocity.

The level of the inside bottom of a drainage pipe at a specific point. Used by drainage engineers to calculate gradients and design drainage systems. Shown on drainage plans and essential for connecting new drainage to existing systems at the correct depth.