Plumbing Basics · 8 min read · Beginner

Basic Plumbing Fittings Explained: Traps, Isolation Valves, Flexi Hoses & Waste Pipe

Recognise the common components found under UK sinks and basins so you know what you are looking at before attempting a small repair.

Key points & steps

A service/isolation valve lets an individual fitting or appliance be shut off for maintenance without necessarily turning off the whole property.
Flexible tap connectors join taps to supply pipework on many modern installations. They must be suitable for the service, correctly sized and not kinked or strained.
A trap is the shaped waste fitting immediately below a basin, sink, bath or shower outlet that retains a water seal against drain odours.
Compression waste fittings seal using shaped washers compressed by threaded nuts, allowing many traps to be dismantled for cleaning.
Waste pipe sizes and fittings vary by appliance and installation. Match the existing nominal size and fitting system rather than forcing mismatched parts together.
Supply-pipe fittings and waste fittings serve different purposes and are not interchangeable even when dimensions appear similar.
If a fitting relates to the incoming drinking-water supply, use products suitable for that application and follow current Water Regulations requirements.

Photograph pipework and labels before visiting a merchant; it is often easier than describing an unfamiliar fitting from memory.
Thread seal tape is not a universal cure for every leaking compression joint; the sealing method depends on the fitting design.
Stop if pipework is badly corroded, unsupported, inaccessible or cannot be isolated reliably.