Allerton’s Good Work Filters Through

7 December 2020

The Problem

Allerton were recently asked to assess a small sewage treatment system serving a domestic property in Lincolnshire. The system is believed to date back from the 1940’s. It was clear from the initial inspection that the system was not operating well. As with all sewage treatment systems, periodic maintenance is required. 

The system is comprised of a single chamber Septic Tank which flowed into a second chamber filled with what was believed to be a blast furnace slag.

As you can see from the pictures, the Septic Tank had not been emptied regularly, the tee pieces which direct the flow of sewage into the Septic Tank and protect the outflow had fallen off and the effluent was only passing over the first 25mm of filter material. It’s not surprising that the quality of the final effluent was not very good!


 Low quality effluent for sewage    Tee pieces missing from Septic Tank

The Solution

Allerton recommended that the following improvements to the system be made:

  • The Septic Tank was emptied and checked for structural defects.
  • New tee pieces and downpipes fitted to the inlet and outlet of the septic tank.
  • Removal of filter bed material.
  • Cleaning of filter bed material.
  • Installation of pipework to improve distribution of effluent over filter material.
  • Best practice adopted by householder regarding use of Septic Tanks.
  • Emptying and maintenance regime implemented.


Very often filter material can be washed and returned to a filterbed which is the most environmentally friendly way of proceeding, but on this occasion the property was in the process of being sold so it was decided to replace the filterbed with fresh filter material.

The Septic Tank was emptied and checked for structural defects and thankfully none were found. While the chamber was empty, a new tee piece and down pipes were fitted. Quite a few Septic Tanks have these tee pieces originally made of vitrified clay. Over the years, the joints become brittle or are knocked by the pipes used for desludging. Either way the results the same, they fall off! This allows raw sewage to flow unimpeded in and out of your Septic Tank. If you have a Septic Tank, it is always worth checking to see if your tee’s are still on.

The only way to remove the filter material was using that summer beach favourite, the bucket and spade. Unfortunately the filter material was in a relatively thin layer and the majority of the chamber was filled with brick rubble, concrete and stone. It was a laborious task with one member of the team in the chamber filling the bucket and passing it through the inspection chamber to a colleague to be emptied. 

                Septic Tank Chamber                                       


As well as the brick rubble, removing some of the filter material also revealed the original distribution arms. In the photo above you can just make out the metal arms on top of the line of bricks. The arms were badly corroded, incomplete, and had been buried. No effluent had flowed over these arms for many years.  

Once the chamber was emptied, it was found to be in good condition structurally with the floor having been covered in clay tiles to prevent filter material being carried out of the chamber. This picture gives some idea of the depth of the chamber. The pipe that can be seen at the top of the chamber is the beginning of the new pipework that we installed.

 Empty septic tank chamber


The chamber was then filled in layers with coke and limestone to form the new filter material. As the existing distribution trays had disintegrated, we created a new distribution system. This system then covered the new filter material 

new filter material in septic tank  with effluent significantly better than the previous system. 

As with all Sewage Treatment Systems and Septic Tanks, regular maintenance is required. It is not always obvious that there is a problem so it is critical that the systems are visually checked.

Be sure to contact us on 01529 305 757 to book a servicing or maintenance appointment for your Sewage Treatment System.