Spherical Septic Tanks

Alpha Septic TankManufactured from GRP, Spherical septic tanks have been the most popular type of septic tank installed in the UK for over four decades and are still today widely available from builders merchants and drainage suppliers.

Designed to be installed completely below ground, spherical septic tanks provide a traditional solution to sewage disposal needs for domestic dwellings without access to mains drainage. 

Sewage enters the spherical septic tank into a settlement chamber, allowing solid waste (sludge) to sink and liquid to rise to the surface.  This surface liquid makes contact with oxygen and the organic matter starts to breakdown biologically.  This liquid still contains sewage but in small enough particles to be carried through the discharge outlet and into the ground (soakaway).

Can I Use A Septic Tank?

Spherical septic tanks only partially treat sewage and discharge effluent of low quality.  Many authorities in the UK prohibit their use.  In most instances a Sewage Treatment Plant should be considered as the first option. Septic tanks may be installed, subject to approval, in applications where:

  • Soil is of suitable porosity.
  • Installation complies with Building Regulations (Approved Document H).
  • The installation will not contaminate any ditch, stream or other watercourse.

Advice Regarding Septic Tanks

If you require advice regarding the installation of a new spherical septic tank or are having problems with your existing tank, contact Mantair for professional assistance on 0800 121 6786 or click here





Case Study - Septic Tank Installation in Norfolk.

Location Cromer Lodge, Felbrigg, Norfolk.

Cromer Lodge, NorfolkNational Trust









Part of the former Gate Lodge to Felbrigg Hall, Cromer Lodge is a quirky, cosy cottage situated at the entrance to Felbrigg Hall Estate in Norfolk.  Guests staying at Cromer Lodge enjoy easy access to park and woodland walks through Felbrigg Estate, whilst the Norfolk town of Cromer is only ten minutes’ drive away.

Septic Tank Survey

Whilst surveying several drainage systems at Felbrigg Estate for the National Trust, Mantair engineers identified that the septic tank serving Cromer Lodge was in need of replacement.

The results of the septic tank survey showed that the soakaway systems connected to the existing septic tank was functioning correctly, allowing the discharged effluent from the septic tank to percolate into the sub strata.

Septic Tank Design

Cromer Lodge is a National Trust Holiday Cottage for persons visiting Norfolk on holiday and as such the variations in flow can alter dependent from high to low seasons.  In view of this and the ground conditions being suitable for a soakaway system, Mantair recommended that a septic tank would be more suitable than a sewage treatment plant.  Sewage treatment plants can be susceptible to variations in flow.

With the soakaway system functioning effectively and the cause of the problem being with the septic tank itself, Mantair engineers recommended that the only remedial works required would be replacing the existing failed septic tank with a modern septic tank. 

With Cromer Lodge being a Holiday Cottage it was essential that all works were carried out and completed during a period when no guests were staying at the cottage.  This septic tank installation in Norfolk was carried out and completed over a period of only two days, ensuring no holiday bookings were affected.

Septic Tank Installation

Prior to any works commencing Mantair engineers scanned the proposed location of the new septic tank to ensure that no underground services were present.

The septic tank was delivered to Cromer Lodge using one of Mantair’s delivery vehicles after it had been inspected at Mantair’s head offices in Essex.  All septic tanks and sewage treatment plants Mantair provides are inspected prior to approval for delivery.

The scope of the works included:

  • Exposing the existing foul drainage pipe work and installation of new drainage to the location of the new septic tank system;
  • Excavation of suitably sized hole in preparation for the installation of the septic tank;
  • Installation of the septic tank, including for a concrete surround;
  • Installing a new discharge drain from the septic tank to the existing soakaway system;
  • Emptying and filling-in of the old septic tank system;
  • Removal from site of all surplus excavated areas;
  • Backfilling all excavations and leaving the area neat and tidy.

Septic TankMantair Septic Tank Installation Norfolk

Septic Tank Commissioning

On completion of the ancillary works Mantair commissioned the septic tank system.

Mantair removed all machinery from site and left the garden area in a neat and tidy manner.

How Mantair Can Help You!

Mantair offers a comprehensive septic tank and sewage treatment plant service. This includes free site inspections, guidance and advice on the most suitable system for the client's requirements, complete installation, commissioning and full after sales care.

Stringent regulations govern the installation of septic tanks, and there are several reasons why a septic tank may not be allowed for installation. Should a septic tank installation not be suitable for your property then a Mantair engineer would guide you through the other “off mains” drainage solutions available.

Click here to view a septic tank installation in Suffolk.

Click here to view a sewage treatment plant installation in Surrey.

Click here to view a sewage treatment plant installation in Berkshire.


For further information click here or Freephone 


0800 121 6786
01255 476 467