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Allflo Underground Drainage

As with most building products, there are a great many suppliers and merchants where you can purchase the products and tools you will need for your projects. For the purpose of this guide, we will be looking at Allflo;

The reasons for which this type of drainage is so revolutionary to the market are listed below:

  • 100% uPVC; (unplasticised polyvinyl chloride) a chemically resistant form of PVC.
  • Brown; as stated with building regulations all underground drainage must be a brown colour, this is mainly for identification purposes to distinguish from other pipework below ground.
  • British kite-marked and BBA approved; it’s very important that the quality and safety of a product is tested and approved by the British Standards Institute and the British Board of Agreement. Allflo has both certificates.
  • Ease of Installation; Allflo is manufactured with the ease of installation in mind, we’ve had feedback from construction professionals and ground workers telling us of the difficulties of fitting the pipes together, the damages if the pipes are not fitted together correctly or are forced together when trying to install.

Underground Drainage Buying Guide

There are two types of drainage systems, as you may already know. The foul water which is all waste from, toilets, baths, kitchen sinks, dishwashers and washing machines; any sewage or grey waste water. And the surface water – this is rainwater only. In some older properties, often the wastewater and surface water will run into the foul water pipes. This is okay, however you will need to ensure that a trapped gully is installed so that no foul air escapes. It is considered best and standard practice when the foul and surface water run into their separate drainage systems.

It is extremely important that you have a clear plan before commencing any work. Where everything will go, how it’s going to connect up and does it adhere to regulations. A diagram can be very useful. You must ensure the underground drainage does not interfere with the foundations of your home or building. You can secure the blueprints of your property from the local council.

Drainage Pipes

The gradient of the pipes has to be correct to ensure the waste and surface water flows properly. The minimum gradient requirements for foul water drainage is 1:40 (if a toilet is connected it should be 1:80) with a 25mm height fall per metre and for surface water drainage is 1:100 and 10mm fall in height per metre of run.

When the pipes need to pass through a building wall, there will need to be a lintel with a clearance of at least 50mm around the pipes. The hole will need to be covered with a rigid sheet to ensure vermin and soil do not end up in your home.

When purchasing pipes for underground drainage always check if they come chamfered on both ends for ease of installation. Our pipes are supplied in either 3 metre or 6 metre lengths and conform to BSEN1401.

Drainage Bends & Connectors

Drain Couplers – Drain couplers are used to join two pipes or plain ended fittings together. It is important with underground drainage to make sure that the rubber seals are intact and are seated correctly. Also, use a lubricant to ease installation and avoid unnecessary leaks.

Standard Bends – These are supplied in double or single socket. Standard bends come in 4 differing degrees; 90, 45, 30 and 15.

Rest Bends – These are used to connect soil stacks and ground floor sanitary appliances to the underground drains. It allows anything coming from the toilet pan to pass through to the drains. The bottom of the bend should never be any closer than 450 mm to the drain floor connection just above the soil stack. The difference between the WC pan outlet and bottom of the rest bend should also be less than 1.5 metres, to ensure that waste can flow smoothly.


PVC pipes are prone to wear and tear over a number of years. This means that from time to time you could be required to carry out some maintenance procedure. Manholes, gullies and chambers should all be installed at accessible points, this way you can clear any blockages, rod the pipework or access any other parts that may need repair work.

When installing gullies, it’s important to check they can withstand traffic that will be passing over them, whether vehicles or pedestrians. If you need greater depth, you may also want to purchase rising pieces. Also sealed lids, if you do want the gully to accept rainwater from the open top grating.

Inspection Chambers

The maximum depth for small inspection chambers set out by building regulators is 600 mm – however, risers can be cut to size if you require them to be shallower.

Inspection chambers are used to access drainage runs and specific points usually when a change of direction occurs. Access allows blockages to be removed, or the system rodded.

Underground Drainage Accessories

There are a number of other tools and pieces of equipment that will be extremely useful and necessary for your underground drainage project;

The pipe chamfer tool; This chamfer tool is becoming widely used and recognized as the safer and more efficient way to square and chamfer 110m plastic pipe. It fits on to your drill and is very easy to use.

Lubricant Gel; It is very important that nothing other than the dedicated lubricant gel for underground drainage is used, should an alternate or other gel be used, the consequences could be leaking and unnecessary damage.

The main purpose of a channel drain is to remove surface water away from a selected area. This helps to prevent flooding and overspill.  The Polystorm-R modular cell is ideally suited for loaded applications at greater depths, such as housing, commercial and infrastructure projects.

Soakaway crates act as a more advanced form of an old-fashioned ditch. Traditionally filled with gravel and used as a place for storm water and excess surface water to soak into. Geocellular crates are manufactured to act as an underground reservoir to collect storm water.





Building Control

Building control must be contacted before starting any work on underground drainage, whether it be installing new drainage or adapting what is already there.

However, if it is a damaged or broken part of your underground drainage, you may fix without permission. It is always best to double check though, you can give them a call on 020 7091 6860.