Plumbing Terminology - L

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A lavatory is a bathroom sink that is permanently installed and connected to a water supply and drainpipe; where you can wash your hands and face, while sometimes used by the general public to mean a bathroom or washroom.

Leach Field

A leach field is an area of porous soil area, through which septic tank leach lines run. Leach fields are used to remove contaminants and impurities from the liquid that emerges from the septic tank.


A locknut is a nut that is fitted into a piece of pipe and screwed onto another pipe to join the two pieces. Locknuts, also  known as a lock nut, locking nut, prevailing torque nut, stiff nut or elastic stop nut, is a nut that resists loosening under vibrations and torque. The first type of locknut used was a fiber instead of nylon and was invented in 1931.

Lockshield Valve

A lockshield valve is fitted at the return side of each radiator and used to balance the system when it is first installed. Generally there is no need to adjust them once set (they are normally covered with a cap), if they are closed to allow for the removal of a radiator, count the turns to the off position so that they can be reset when required.

Low Level Cistern

A low level cistern is a tank that is mounted on the wall just above the toilet pan with a short flush pipe. Generally the cistern is operated by a lever mounted on the front of the tank or (more modern) a push button on the cistern top cover.