Drainage

Explore drainage in plain English, with practical context, common distinctions and questions to ask before work starts.

Start with the entries below. They are part of a growing reference library, not an exhaustive technical specification or a substitute for specialist assessment.

Air admittance valve

An air admittance valve, or AAV, allows air into a suitable drainage arrangement when negative pressure occurs, helping protect trap seals. It is not a general-purpose extractor and does not provide an open outlet for positive pressure or sewer gases. Suitability depends on the whole drainage design.

CCTV drain survey

A CCTV drain survey uses a camera to inspect accessible drainage pipework and record visible condition, connections and obstructions. It can help investigate recurring blockages, inform repairs or support a property purchase. The camera provides evidence within its reach and visibility; it cannot prove the condition of every buried pipe by itself.

Drain relining

Drain relining repairs suitable existing pipework by installing a specified lining system rather than excavating and replacing every affected section. It can be useful in appropriate conditions but does not correct every collapse, level defect or access problem. Suitability depends on investigation, pipe condition, connections and the intended design.

Getting into drainage work

Drainage work spans installation, investigation, maintenance and repair of waste and surface-water systems. Clearing a blockage, designing a new drainage layout and relining an existing pipe are different activities. A useful entry route defines the intended job and develops practical competence without treating every chamber as a safe place to enter.

Soakaway

A rainwater soakaway is an underground structure that temporarily stores surface water and allows it to infiltrate into suitable surrounding ground. Its capacity comes from usable void space and the ground’s infiltration characteristics. A hole filled with random rubble is not automatically a correctly designed drainage system.

Last editorial check: 8 November 2026.