Drain Dictionary

Blockages & Causes

What goes wrong inside drains — and the terminology used to describe it.

Backfall A section of drain that slopes the wrong way, so water runs backwards or pools instead of draining. A common defect found during CCTV inspections. Bellied Pipe A sag or dip in a run of pipe where the bedding has settled, leaving a low spot that permanently holds water and collects debris. Blocked Drain Any drain where flow is stopped or restricted — by roots, fat, foreign objects, collapsed pipe or scale — causing slow drainage, gurgling, odours or overflows. Collapsed Pipe A pipe that has structurally failed — crushed, broken apart or caved in — so the bore is partly or fully closed. The most serious drain defect. Concrete in Drain Cement slurry or concrete that has entered a drain during construction work and set hard inside the pipe — one of the toughest blockages to remove. Cracked Pipe A pipe with fractures in its wall — circumferential, longitudinal or multiple — that leak wastewater out, let groundwater and roots in, and weaken the pipe stru Displaced Joint A pipe joint where the two ends have moved out of alignment, opening a gap or step that leaks, catches debris and invites tree roots. Exfiltration Wastewater leaking out of a drain into the surrounding ground through defects — often invisible at the surface until smells, damp patches or subsidence appear. Fatberg A congealed mass of fats, oils and grease (often combined with wipes and debris) that hardens inside drains and sewers, restricting or fully blocking flow. Infiltration Groundwater leaking into a drain through cracks, joints and defects — adding constant flow, washing in soil, and overloading sewer systems in wet weather. Ovality Deformation of a flexible pipe from round toward oval under ground load — measured as a percentage, with excessive ovality signalling bedding failure and future Scale Build-Up Hard mineral deposits (calcium and magnesium salts, or iron-based encrustation) that accumulate on pipe walls over decades, narrowing the bore. Vermin in Drains Rats and other pests using damaged drains as highways and entry points into buildings — a hidden defect symptom as much as a pest problem. Wet Wipes Blockage Blockages formed by wipes marketed as "flushable" that do not break down like toilet paper, instead knotting into ropes and mats inside drains and pumps.

More Categories

Pipes & Materials (4) Drainage Structures (8) Inspection & Technology (9) Repair Methods (6) Cleaning & Clearing (3) Plumbing Fixtures (3) Sewer Systems (8) Stormwater (8) Trade Terminology (5) Regulations & Standards (5) Water Flow & Hydraulics (5) Tree Roots & Vegetation (2) Maintenance & Prevention (1)

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