What is a soakaway?


A soakaway is a very effective way of dealing with surface water.  Traditional soakaways collect all the surface water run-off into one point and then allow the water to percolate in a controlled manner into the surrounding ground/earth in the area where it falls.  A soakaway drain feeds the water into the central collection point.


The two types of Soakaway:



Surface water soakaway


Surface Water Drains are used to carry away rainwater from gutters, patios & driveways etc.  The rainwater, which is not contaminated and hence is not harmful, will be transported to a soakaway.


These soakaways are usually some form of "crate" system with a holding capacity during particular heavy downpours or prolonged rainfall.


 If the ground is not suitable and you install a soakaway then water logging occurs and can contribute to localised flooding, so it is important to do the homework before attempting to install a soakaway...


We at Evolution Drains assess the requirements of each job separately... No particular soakaway will ever be suitable for every property, we meticulously design each system to be as efficient as can be for our clients individual needs...


Surface water soakaways are initiallty sized via a percolation test to gauge the porosity of the ground, then the volume of water predicted and then the system is calculated as to what size will be required. 



Foul soakaway


Foul Drainage is the system of pipework that carries waste water away from a bathroom, kitchen or utility room.


The Soakaway is an extension of the treatment system. The Soakaway is required to be within the top 1m of the ground where there is the most oxygen, this helps the bacteria that is required to continually break down the waste within the effluent thrive and multiply, cleaning the waste further prior to discharge into the ground.


Once again a porosity test of the ground is required to establish how quickly water will disperse in the ground.  There is a specific calculation to establish sizing for use with a septic tank or a treatment plant...


We at Evolution Drains assess the requirements of each job separately... No particular soakaway will ever be suitable for every property, we meticulously design each system to be as efficient as can be for our clients individual needs.


Foul soakaways are typically constructed using a trench system with stone and solid perforated pipe. There is also the option to use "tunnels" with a "bio" Mat.

We are proud to introduce the Polybed Drainage System: an alternative to traditional soakaway methods, which is sustainable and offers high performance.


It offers the following key benefits:



Good for the environment


  • The system is manufactured using 100% recycled materials
  • Reduces site traffic – one truckload of Polybed is equivalent to 8 trucks of gravel
  • Cuts out the need to quarry and transport aggregate – just one 3m length of Polybed does the same job of a quarter tonne of gravel
  • Reduced need for soil cart-away.





  • The Polybed System is extremely lightweight and delivered as complete, ready-to-use units which are easily joined with a rapid click-fit connection
  • No specialist skills required to install and use, which reduces Health & Safety risks
  • Ideal for use in restricted areas
  • Can be routed around existing garden features.





  • The Polybed Drainage System is up to 4 times quicker to install than traditional soakaway methods
  • Less labour and plant is used in installation
  • Stone and gravel usage is minimised
  • Transportation costs are lower.
  • High performance
  • Infiltration is controlled
  • Flow capacity is high
  • Consistent void ratio in excess of 30%.

Case Study

Polybed products – a proven solution

Polybed is not solely for commercial use. Its versatility and ease of installation makes it a popular choice with private clients too.

When Forest Group director Chris Price and his wife Sue encountered on-going problems with their septic tank, they turned to Polybed for a solution.


The Prices’ bungalow is beautifully situated high in the Cotswold Hills, but access to the rear of the property is extremely restricted. There is no vehicular entry and the only external way in to the back garden is via a narrow stepped passageway to the side of the building.


Having no mains drainage, the family were dependent upon an ageing septic tank – unfortunately located in the lowest part of the back garden – for waste and sewage disposal. The tank overflowed on a regular basis as the filter field had become clogged over many years of use.

The restricted access for heavy machinery made replacing the tank impractical. As the basic structure was sound, Chris installed a unit to convert the septic tank into a small package treatment plant. He then created a more effective filter field under his lawn using Polybed.


21 units of 3mlength Polybed were laid in a network of 600mmdeep, 300mmwide trenches dug by hand. A covering of geotextile permeable fabric was used to protect the units from soil and, to minimise mess, each trench was backfilled with the earth from the next and the turf immediately replaced.


The Prices are delighted with the result. “The whole project took just 3 days, and the majority of the time was taken up with digging the trenches”, said Chris.

“It only took a couple of minutes to install each Polybed length. Unfortunately I was suffering from rheumatism that week so Sue had to help with the carrying. We were amazed how light the units were and how quickly they were installed. Within a very short space of time the lawn was back to normal and you wouldn’t know we’d had anything done at all.”