Glossary

Channel drain, Line drain, Slot drain and ACO drain

These terms are often used interchangeably to refer to drains of a linear nature. ACO is actually the brand name of the leading global manufacturer of drainage solutions.

Thus, the ACO name has become synonymous with this type of drain. Think of it as the Hoover of channel drains.

Channel drains are channels with a grating on top. They are designed to use their entire length to drain surface water from a hardstanding area, such as a driveway.

Channel drainage products are all given a Load Class which refers to the weight they can withstand in use. Domestic ACO drainage products have a Load Class of A15, meaning that they can withstand a load of 1.5 tonnes and are suitable for a domestic driveway drain.

What is a Durgo Valve?

Durgo is actually the Swedish patent name for their air admittance valve. The Durgo Valve name has now become synonymous with this type of valve (think of it as the Hoover of channel drains).

It is a one-way air vent is installed on above ground vertical waste pipes such as a stub stack so that when it is drained (e.g. a toilet being flushed), clean air can enter but foul smells and gasses will not escape and is designed to prevent gurgling, etc.

Air pressure testing is, scientifically, called a hydrostatic test. The test involves filling a vessel or pipe system with a liquid, usually water, which may be dyed to aid in visual leak detection, and pressurization of the vessel to specified test pressure.

Pressure tightness can be tested by sealing the airline once pressure was induced to the system, and observing whether there is a pressure loss.
This is one of the many methods plumbers and drainage engineers can test for leaks in your pipe system.

Other methods include water testing and sound testing.

Pipes, fittings and joints should be capable of withstanding an air test of positive pressure of at least 38mm water gauge for at least 3 minutes. Every trap should maintain a water seal of at least 25mm.

Smoke testing may be used to identify defects where a water test has failed. Smoke testing is not recommended for PVC-U (plastic) pipes.

The anti-flood valve which can be installed anywhere on the main line drainage run. They are normally found just before the drainage system crosses the boundary line or in a basement just before the pipework leaves the curtilage.

The modern materials used on these valves prevent corrosion and deterioration, however it is recommended that the units are annually inspected to ensure operation is not hindered by build-ups of silt or debris.

How Anti-Flood Valves Work

Anti-flood valves come in a pre-formed chamber where floats sit on either side of the inlet pipe.
When the water level rises, the floats lift and rotate the drain stopper over the inlet. This shuts off the upstream system.

These valves are extremely effective and as the drain stopper is out of the way during normal operations, they are suitable for both combined and foul drainage systems.
Unlike many of anti-flood devices that simply rely on a flap that hangs in the pipework, they do not hinder the flow of water and waste.

Like soakaways, attenuation tanks are installed to hold rainwater however cover a much larger area. They are designed to hold a high volume of water during very heavy rainfall which in a normal system would overload the main sewer have a flow control chamber which releases the stored water before running into the drainage system.

Although this looks like a standard gully at ground level, this design has below ground connections and therefore the connecting pipework does not discharge onto the grating.

During the installation of some systems, the pipework has not been laid to a good falling gradient, sometimes flat or with the downstream section higher than the direction the water is coming from and where the water is not flowing away it is pooling which causes the accelerated accumulation of debris deposits. These problems are usually impossible or too expensive to remedy and therefore the only option is likely to be regular maintenance. The ideal fall is 1 in 40 for 100mm pipework and 1 in 60 for 150mm.

Branch (or lateral) connections are drains that are not the main section of pipework running upstream and downstream but a drain that connects to the side of either a manhole chamber or underground section of pipework. Most manholes have connections joining in and this is usually adequate access to carry out a CCTV camera inspection however this is not possible if the connection is underground as the camera unit is unable to navigate bends such as these. Most connections are made with the correct junctions either during the time of installation or whilst carrying out alterations however it is common to see “DIY” jobs where it has been made by simply breaking open the existing pipework and adjoining the connecting drain by means of a cement joint. It is most likely that these type are not watertight.

Similar to an interceptor trap and inline trap, Buchan traps were installed in Victorian times to prevent the escape of foul smells and vermin from the communal sewers however as they are not accessible from a manhole and only have a rodding access point at ground level, there are usually difficulties clearing blockages which are known to build up in the u-bend of traps. When a Buchan trap is found to be damaged and needs to be replaced, this is usually an expensive job as typically they are between 2.0-3.0m deep and are located in narrow front gardens.

A way to prevent internal flooding during a blockage was the installation of a Burns chamber which is where a metal plate is secured within the manhole chamber under the cover to stop water rising and overflowing. Burns chambers are only incorporated as part of a cast iron drainage system and are sealed with metal bolts which can be opened when access is needed for cleaning, investigation or repair works.

A catchment pit is an empty chamber installed in the surface water drainage system for intercepting silt and debris deposits being carried along the pipework. This works by having a high level inlet pipe which allows the water to rise to discharge through the outlet pipe also positioned at a high level, leaving sediment sitting at the bottom which will require regular cleaning to avoid blockages.

Do I need a CCTV drain survey? In most cases, yes. CCTV Drainage Surveys are camera inspections. They allow information to be gained regarding the underground system including the pipework diameter and if there are any branch connections, all of which are pertinent when deciding the best drain repair technique. There are a number of reasons a drain survey may be carried out and you can see these here. Find out more about CCTV Home buyer’s survey.

A cesspool, sometimes referred to as a cesspit, is a type of wastewater system that is essentially a sealed underground tank where sewage is stored and not treated. It collects all waste and wastewater from a property and has to be emptied on a regular basis to avoid overflow or leakage. Unlike septic systems, there is no outflow from a cesspool and it doesn’t perform any kind of wastewater treatment.

Many drainage systems are of earthenware or clay construction and although strong, it is a material known to fracture. A circumferential fracture runs around the circumference of the pipe and will allow the loss of water into the surrounding ground area, possibly leading to subsidence. These fractures are usually easy to repair by drain lining/sleeving if there is adequate access but they can deteriorate over time if left and could result in a collapse where excavation will be required to carry out the repair.

CIPP (Cured In Place Pipe) is a cutting-edge technique that enables the effective rehabilitation of sewers and culverts, without having to carry out costly open-cut excavation and replacement of the pipe. In general, quality CIPP drain lining is less disruptive, better for the environment, safer and, almost always, more cost-effective. We can repair pipelines ranging from 100mm to 600mm in diameter.

Although manholes are for providing access to the drainage system, some properties have built over them and therefore rendered the chamber useless. This is not advisable as in the event of an emergency blockage, engineers would have difficulty clearing it without full access. These also prevent inspections and maintenance being carried out to any connecting pipework. In numerous cases, expensive kitchen floors have to be broken up to access these chambers.

Surface Water Drainage Strategies are frequently conditioned as part of planning permission, and show how surface water runoff from the site can be managed to comply with the requirements of the NPPF, the Environment Agency or local planning policy.
It is becoming increasingly important to demonstrate to the Local Planning Authority, the Lead Local Flood Authority, and the Environment Agency that surface water drainage has been considered.

Drainage surveys are CCTV camera inspections. They allow information to be gained regarding the underground system including the pipework diameter and if there are any branch connections, all of which is pertinent when deciding the best drain repair technique. There are a number of reasons a drain survey may be carried out and you can see these here

A drop shaft, in the context of drainage and sewer systems, is a vertical pipe or structure used to lower the level of flow in a system. It allows for the transfer of water or wastewater from a higher elevation to a lower one, typically to overcome differences in topography or to connect different levels of a sewer system. The design of a drop shaft aims to minimize turbulence and potential damage to the system while ensuring efficient flow.

Also known as exterior drop connection or back drop connection

As foul smells and sewage from a blockage can escape through the edges of a manhole cover, the standard design is not permitted to be used internally and Building Regulations state a bolt down, double sealed cover and frame needs to be used as it is airtight.

This one-way air vent is installed on above ground vertical waste pipes such as a stub stack so that when it is drained (e.g. a toilet being flushed), clean air can enter but foul smells and gasses will not escape.

If the configuration of the drainage prevents passage of the camera, fluorescein dye is dropped into the system to confirm a connection. You can read more about tracing methods here.

French drains are for subsurface water. To not be confused with gulley or rain water down pipes which are form surface water. They are used in areas that stays soggy for days and even weeks after rain events. Very common problem in hilly areas, especially with retaining walls. These are trenches with a pipe in the bottom. The pipe has holes in the bottom and the trench is filled with gravel. The water flows into the gravel, down to the bottom of the trench and into the pipe which in turn, must discharge to a drainage system, like a soakaway, or the actual surface water drainage system. It is not a suitable replacement for a surface water drainage system.

Whilst CCTV drainage surveys allow us to see what is happening underground, it is not always possible to determine where the pipework is. Tracers are inserted into the pipework and tracked above ground and are used to pinpoint certain areas such as a concealed manhole or a collapsed section. You can read more about this service here

Foul water is wastewater serving a bathroom, kitchen, or utility room and is discharged into communal sewers, septic tanks, or cess pits. New drainage systems are separated into foul water and surface water where possible to help with the level of waste that needs to be treated before being released back into the environment and therefore combined systems that take both are mainly found in older properties. Foul water cannot discharge to a surface water system or soakaway due to its contaminated waste and the Environmental Agency and Local Water Authorities can issue correction notices and fines if these illegal, unhygienic misconnections causing pollution are found. So-called “grey water” which only serves sink wastes, etc. is also classed as foul water and cannot be discharged into a separate Surface water system or soakaway.

The gradient (or fall) is the term used to denote the distance that a pipe drops vertically relative to its horizontal length – essentially the slope of the pipe.

Gullies are often found at the base of above ground sections of pipework such as a kitchen sink waste pipe or rainwater pipe connecting to the underground system with a trap to prevent the escape of foul smells and rats. They are also used in large external spaces to drain surface water from the ground into the drainage. Newer gullies are designed with a rodding access which allows for cleaning and investigation works to be carried out beyond the trap should the need arise. Gullies are usually identified by the small circular or square grid at ground level.

Standard manhole covers are not aesthetically pleasing and therefore it may be decided that a recessed cover is used as they allow for bricks or slabs to be installed to match the surrounding area, making it blend in to the floor but still allowing full access.

These covers are manufactured in galvanised steel; factory filled with reinforced high-strength concrete and badged to customer requirements. They are designed with manual handling safety in mind, featuring tapered sides and centralised lifting keyholes.

Interceptors are a common name for Running Traps, Buchan Traps, and Winser Traps.

These are usually found in the outlet of the last manhole chamber and this is the favoured design to prevent the escape of foul smells and passage of vermin from the communal sewers as there is incorporated rodding access. This is beneficial as it is quite common for the traps to block up but these are usually cleared with ease.

Similar to an interceptor trap and Buchan trap, inline traps were installed to prevent the escape of foul smells and vermin from the communal sewers however as they are not accessible from a manhole and do not have rodding access, there are usually difficulties clearing blockages which are known to build up in the u-bend of traps.

These drains are channels which have a grating over the top and are designed to drain surface water from a hardstanding such as a driveway along the entire length instead of from one point like a yard gully. We advise regular maintenance is carried out to these as leaves and other debris can build up which was cause the water to drain away slowly and possibly overflow.

Lateral (or branch) connections are drains that are not the main section of pipework running upstream and downstream but a drain that connects to the side of either a manhole chamber or underground section of pipework. Most manholes have connections joining in and this is usually adequate access to carry out a CCTV camera inspection however this is not possible if the connection is underground as the camera unit is unable to navigate bends such as these. Most connections are made with the correct junctions either during the time of installation or whilst carrying out alterations however it is common to see “DIY” jobs where it has been made by simply breaking open the existing pipework and adjoining the connecting drain by means of a cement joint. It is most likely that these types are not watertight.

Many drainage systems are of earthenware or clay construction and although strong, it is a material known to fracture. A longitudinal fracture runs down the length of the pipe usually from a joint and will allow the loss of water into the surrounding ground area, possibly leading to subsidence. These fractures are usually easy to repair by drain lining/sleeving if there is adequate access but they can deteriorate over time if left and could result in a collapse where an excavation will be required to carry out the repair.

The main purpose of a macerator such as a Saniflo (common brand) is to break up solid waste with blades, making it easier to pump the liquid sewage uphill or vertically. They are most commonly used in basement toilets where it is not possible to install a gravity system. In our opinion, although they have improved in recent years, they are not always reliable and need replacing every couple of years.

This refers to the connection from a property to the public sewer system. It is the pipe that carries wastewater and sewage from the property into the public sewer for treatment at a wastewater treatment plant. A mains sewer connection is generally preferable to private systems like cesspools or septic tanks because it doesn’t require the property owner to maintain a private wastewater treatment system.

Obstructions in the drainage system restrict the free flow of waste and the camera unit will be unable to pass it when carrying out a drain survey. Water usually holds behind an obstruction which prevents a clear view of the cause however it can be anything from a build up of non-disposable wipes and nappies, a roots mass or collapsed section of pipework.

An offset joint occurs when two sections of earthenware pipework are connected but were not aligned properly during installation. An offset joint does not necessarily leak as the cement fillet of the joint may be intact.

Pitch fibre was a material used predominately in the 1960’s and was subsequently found to be inherently defective, becoming deformed and blistered over a period of years. Moderate stages of deterioration require rerounding & Patch Lining. Advanced stages of the “squashing” cause the pipework to block completely, requiring excavation and renewal.

Property owners are only responsible for the drains within their boundary lines that serve only their property. Once these sections of drainage cross the boundary line either under the pavement or into a neighbouring garden, etc., they fall under the ownership of the Local Water Authority.

Many existing drainage systems are of earthenware or clay construction and while strong, they are known to fracture. A radial fracture runs partly around the pipe and will allow the loss of water into the surrounding ground area, possibly leading to subsidence. These fractures are usually easy to repair by drain lining/patching if there is adequate access but they can deteriorate over time if left and could result in a collapse where excavation will be required to carry out the repair.

Marine-grade steel rat blockers are usually installed in place of interceptor traps. This is to prevent the passage of vermin from the communal sewers into the private drainage system. These require annual maintenance to ensure that the hinged flap continues to operate satisfactorily. These are usually used as an economic alternative to replacing the defective interceptor trap.

Standard manhole covers are not aesthetically pleasing and therefore it may be decided that a recessed cover is required. They allow for bricks or slabs to be installed to match the surrounding area. The resulting lid blends into the floor while still allowing full access.

These covers are manufactured in galvanised steel. They are factory filled with reinforced high-strength concrete and badged to customer requirements.

They are designed with manual handling safety in mind, featuring tapered sides and centralised lifting keyholes.

During house renovations, it is possible that some drains no longer have a use. They are often forgotten about and left open. When not forgotten, they are not sealed properly. We advise these runs are sealed at the manhole chamber. Rats prefer to nest in these sections and can escape inside your household.

Pitch fibre pipework is prone to “squashing” and therefore rerounding can be required. Rerounding is a technique used to return the drain to its original circular shape.

Vertical downpipes that do not discharge to a gully are connected to the underground system with a rest bend. The 90° bend has a long sweeping angle. It allows the waste to flow smoothly and has a footing to help absorb the force of the flushed water.

Rodding eyes (or rodding accesses) are found on interceptor traps, new-style gullies, and some sections of above-ground pipework to allow entry to the drainage system, mainly to attempt to clear a blockage however CCTV camera inspections can also be carried out from these points. They are sealed with caps to prevent the escape of foul smells and vermin and these should be able to be removed when needed and not be cemented into place. Whilst they do provide access, this is usually limited and we do advise there is further access in the form of a manhole.

The main purpose of a macerator such as a Saniflo (known brand) is to break up solid waste with blades, making it easier to pump the liquid sewage uphill or vertically. They are most commonly used in basement toilets where it is not possible to install a gravity system. In our opinion, although they have improved in recent years, they are not always reliable and need replacing every couple of years.

To ease the burden on sewers, rainwater can discharge to soakaways which is simply pipework connecting to a hole in the ground (at least 5.0m away from the building) filled with crates wrapped in non-woven Geotextile membrane and holds water, allowing it to disperse back into the earth slowly. This is a modern alternative as previously the hole used to be filled with rubble. This prevents water logging in the garden, stops damp seeping into the property and can save you money on your water bills. Because of the limited access, soakaways are difficult to repair and may need to be replaced if damaged.

In the utility locating industry, sondes are radio transmitters that are used to locate non-metal underground utilities or assets like sewer pipes, storm drains and buried chambers. When used with video inspection cameras, these transmitters can pinpoint the location of blockages and pipe defects, allowing for a localised CIPP Patch Liner repair. Sondes are also helpful for improving inaccurate or incomplete utility maps.

As drainage systems need some ventilation to allow the escape of gasses, most properties have a soil and vent pipe where the top of the pipe is open to let air circulate. This usually serves upstairs bathrooms and Building Regulations state that the pipe must extend up to at least 1.0m above eaves level.

SuDS (short for Sustainable Urban Drainage Systems) show how surface water runoff from hardstanding areas can be managed to comply with the requirements of the NPPF, the Environment Agency, or local planning policy. These surface water drainage strategies are becoming increasingly required as part of planning permission. This is one of the areas we specialise in.

These are short sections of above-ground pipework that serve waste pipes and toilets (similar to a soil and vent pipe) but do not extend to the top of the property with a vent.

Surface Water is clean rainwater that enters the drainage system through guttering and yard gullies, etc. and as it is not contaminated so doesn’t require treatment, it can discharge into a soakaway, stream or river. New drainage systems are separated into foul water and surface water where possible to help with the level of waste that needs to be treated before being released back into the environment and therefore combined systems that take both are mainly found in older properties. Foul water cannot discharge to a surface water system due to its contaminated waste and the Environmental Agency and Local Water Authorities can issue correction notices and fines if these illegal, unhygienic misconnections causing pollution are found.

Swan necks are used in vertical downpipes to allow for a difference in the structure of a building such as the gutter on the edge of a roof to the rainwater pipe adjoined to the wall.

Whilst the pipework needs to be laid to a good gradient for water to drain away, the fall cannot be too sharp. If the downstream manhole is in a lower ground area, the drain is usually laid to the correct gradient, but has a vertical section of pipework connecting it to the channel. This is similar to a vertical backdrop with the difference being this vertical section of pipework is inside the chamber walls.

Whilst drain surveys can show us if there are any fractures in the pipework, they do not show us how much water is leaving the system. Carrying out a water test by capping off a run at the manhole then filling the drain with water determines whetehr the pipework is sealed, and if not, based on the drop of water, it can give a good indication into the extent of the damage.