Why do we Need Soak Pit Tank ?

Why do we Need Soak Pit Tank ?

The water in the septic tank is not pure, it is called grey water because it still contains organic materials that need to be filtered out.  A Soak Pit is a covered, porous-walled chamber that allows water to slowly soak into the ground. Pre-settled effluent from septic tank is discharged to the underground chamber from where it infiltrates into the surrounding soil.

Soak PitDesign

A layer of sand and fine gravel is spread across the bottom to help disperse the flow. Depth should be between 1.5 and 4m deep, but never less than 1.5m above the ground water table. The Soak Pit is filled with coarse rocks and gravel. The rocks and gravel will prevent the walls from collapsing, but will still provide adequate space for the waste-water.


As waste-water percolates through the soil from the soak pit , small particles are filtered out by the soil matrix and organics are digested by micro-organism.

Soak pit are best suited to soils with good absorptive properties; clay, hard packed or rocky  soils are not appropriate.


A Soak Pit does not provide adequate treatment for raw wastewater and the pit will clog quickly. A Soak Pit should be used for discharging pre settled black water or grey water.

Soak pits are appropriate for rural and suburban settlements. They depend on soil with a sufficient absorptive capacity. They are not appropriate for areas that are prone to flooding or have high groundwater tables.

Health Aspects

The technology is located underground and  thus, humans and animals should have no contact with the effluent. The Soak Pit is located a safe distance from a drinking water source (ideally 30m).  The Soak Pit is odourless and not visible.

Soak Pit Schematic Diagram
Soak Pit Schematic Diagram A-masonry ring B-stone or brick aggregate C-brick chamber D-30cm thick outer casing with coarse sand E-effluent from septic tank


  •  the effluent should be clarified or filtered well to prevent excessive build up of solids.
  • The Soak Pit should be kept away from high-traffic areas.
  • Particles and biomass will clog the pit so need to be cleaned or moved.
  • For future access a removable  lid should be used to seal the pit.


  • Can be built and repaired with locally available materials.
  • Small land area required.
  • Power conservative.
  • Can be built and maintained with locally available materials.
  • Simple technique for all users.


  •  Pre-treatment is required to prevent clogging, although eventual clogging is inevitable.
  •  Negatively affects soil and groundwater properties.

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