Technical Glossary

Drain & wastewater jargon explained:


A generic term for a ‘rotating biological contractor’ or packaged type of sewage treatment system.

Check or Non-return Valve

A non-return valve lets flow go in one direction only so can be used, for instance, to stop contaminated water getting into a clean water supply. It works using pressure.


Curing or hardening resin in the liner creates a new pipe inside the old pipe. Hot water, ambient temperature or UV-light methods may be used to carry out the process.

Drain Cleaner

Chemical products or devices (like plungers) may be used to remove ‘soft’ drain obstructions caused by the build up of soap, hair and grease.
Serious blockages affecting a whole drain or lateral connections will be tackled by a drain cleaning specialist using high-pressure water jetting equipment. Note that chemicals can react with water or metals, giving off vapours which could cause health hazards. Always read manufacturer’s instructions.

Drain Fly

Insects which like the moist conditions and decaying matter which can be found in drains, or where there are leaks. They are unpleasant but generally harmless.


A mixture of wipes, period products, fats, oils and grease that congeal into a solid mass in drains and sewers.


Fats, Oils and Grease unwanted things poured into the drains and sewers

Foul Sewage

Sewage is the liquid or effluent from sinks, baths, showers, kitchens and toilets in domestic properties.

Inflatable packer

Used to position a patch repair liner and force it against the internal surface of a damaged pipe. Once cured, the repair forms a new section inside the pipe.


The method by which the impregnated liner is installed. The tube liner is forced through the damaged pipe by water pressure. At the same time, the water turns it inside out pushing the resin impregnated side outwards to adhere to the inside of the pipe, sewer or drain.


The ‘tube’ of material (often special felt or a fibre glass matrix) manufactured to a given length and diameter. This is installed in the sewer or pipe to create a new pipe inside the damaged one.

Macerator Toilet

You can install a macerator toilet (like a Saniflo) even though there is no access to a standard foul discharge pipe. The macerator pulverises solid waste and toilet paper into a liquid so that it will go through pipes as small as 25mm diameter. Note that the waste will still need to discharge into the foul sewage system, not the surface water drain.


Similar to a liner, but used for isolated defects or small damaged areas within a drain, sewer or pipe.

Primary Settlement Tank

The tank where the majority of solids settle and are removed from the crude sewage that flows into the primary settlement tank.


Wipes, period products and any unwanted items found in the drains and sewers.


The method of repairing a drain or sewer by creating a new pipe within the existing one, without the need to excavate. Also known as ‘no-dig’ or ‘trenchless technology’.


The liner is impregnated with resin prior to being installed. The resin then hardens (cures), creating a new pipe inside the old one.

Resin Injection

Used to stop water ingress in manholes. Polyurethane resin is injected into the manhole where it expands to 40 times its original volume on contact with water, sealing the holes and cracks.

Sanitary Sewer or Sewer Network

The sewer network takes foul wastewater or sewage to a treatment plant. Sewage is carried from houses and buildings via lateral drains, first to a branch sewer then to a main sewer. Manholes allow access to the sewers for inspection and maintenance, and to vent sewer gases.

Secondary Settlement Tank

The tank where humus (organic matter) is separated from the effluent/liquid that flows through it, from biological filters or other biological treatment units.

Separate System

A drainage system that has one pipe network for foul water and another for surface water.

Septic Tank / Cesspit

When a building has no connection to the main sewer network, a septic tank is installed to collect wastewater from the house. Inside the tank, the waste separates and degrades using bacterial processes, so that the naturally cleansed liquid drains out into a soakaway or drainage field, whilst the solids remain in the tank. The resultant sludge should be removed at regular intervals — typically every year.
A cesspit is a simple holding tank for foul waste which needs to be emptied by a specialist contractor.

Sink Macerator

Waste disposal units or macerators used to be seen as a convenient way to get rid of food leftovers instead of sending it to landfill.

With recycling methods and a better understanding of what should and shouldn’t be put into the drains, food macerators are considered poor practice. Not only can food and FOG (fat, oil and grease) cause blockages if disposed of down the drains, they may also encourage rats and mice.

From 2018, new legislation will ban sink macerators from commercial kitchens in England and Wales. They are already banned in Scotland and Northern Ireland.


Sludge is a mixture of solids and water that is produced during the treatment of wastewater and sewage in private systems or the public wastewater treatment works (WwTW). Sludge has to be removed from a treatment system by a process known as de-sludging.

Soil Vent Pipe

Also called a soil stack or drain-waste-vent (WV), a soil vent pipe (SVP) carries foul waste (sewage) from the different floors of a house into the underground sewer network. It extends up to roof level to allow sewage smells to release into the atmosphere. SVPs are usually fitted externally, but can be installed within the wall cavity.

Storm Drain

Storm drains take excess rain water from streets, car parks, drives, road gulleys, footpaths and roofs — anywhere the water can’t just drain away into the ground. Most connect directly to the surface water drainage system, but some may join a ‘combined sewer’, which becomes part of the foul waste system.


The most common form of ‘trap’ plumbing is a U-bend (as invented by Thomas Crapper), though there are also P- and S-bends. All plumbing fixtures must have a trap, either inside or out. The trap holds standing water to stop sewer gases getting inside the property, but still lets waste through to the sewer system. The standing water creates a seal, refilling each time the toilet/sink/bath/etc is used.

Water Table

The term ‘water table’ refers to the amount of water below ground. During flooding the water table is described as ‘saturated’.

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