Saturday, 10 December 2016

Constructing Soak-away Pits/Septic tanks that never fills up - Engr. Osaz' ENOBAKHARE

When a septic tank gets filled up, it tends to put a frown on the users’ faces; not necessarily because the worst thing just happened but because they start feeling the nauseating odour almost immediately and then the cost of transferring the wastes comes to mind. They must invite a waste disposal agent to do the needful or else they will be unable to use their closets! Well, those days are winding out fast with the introduction of soak-away pits or septic tanks that never fills up.  

Just in case you are wondering if there is any difference between a septic tank and a soak-away pit: A septic tank is designed and built like an underground tank or container usually with reinforced concrete, blocks or bricks. Essentially, it is closed on all faces with a small opening only at the surface to allow the escape of waste gases and for a hose to penetrate during pumping-out operations. It is highly recommended in areas with high and moderate water tables (e.g. from 0 - 10m from natural ground level) and areas susceptible to flood. On the other hand, Soak away pit are useful in areas of low water table.

They are built such that they are only covered at the top and sides. The bottom is left uncovered so that the waste water will soak away naturally into the earth leaving the solid wastes behind which begins to decompose as soon as the pit becomes fairly dry.  Like Septic tanks, a little portion is cut open on the top to allow for the required ventilation that aids the drying out process within the pit. These portions are usually protected such as will not permit the passage of rain or surface water into the interior of the pit or tank.

Modern septic tanks or soak-away pits are built like wells within a small diameter of about 1-metre thereby saving space while maintaining its functional requirements. The joints in such systems are adequately sealed, the bottom surface of the first rim below is well compacted and blinded before the rim is placed and subsequently loaded. 

The back fill is also properly done to prevent excessive deflection. For septic tank, the entire bottom is covered but the reverse is the case with soak-away pits. With the aid of a drilling machine, a hole of about 75mm is drilled at the side of the topmost rim above ground level to accommodate a pipe that will convey waste water that rises to that level into a chamber just beside the pit. A pipe is also connected in a similar manner to the other end of the chamber which conveys treated waste-water directly to the nearby drain (otherwise referred to as gutter). 
Soak-away Pit or Septic Tank constructed with Reinforced Concrete Rims
Special Chamber for treatment of Sewage/Waste water

Within the chamber, a net trap is fixed at the entry point of the pipe to ensure that no solid waste is allowed to be passed into the chamber. The chamber is constructed in such a way that allows the user of the system add a bio-pod or pour camphoric oil or other approved eco-friendly mixtures into the chamber to treat the waste water before it is allowed to flow into the pipe that takes it directly to the public drain. These mixtures are very cheap and readily available. A lock and non-return valves are built into the exit point of the chamber so that the user can control when the treated waste-water would be allowed to flow out of the chamber. The process can be carried out at any time of the day.

This concept is based on the fact that the solid waste matter in septic tanks/soak-away pits are very little in relation to the space they occupy even after many years i.e. if waste water only is drained out of the system, the volume of solid waste (shit stuffs) left is often insignificant. It is believed that if you can get the waste water out through a natural process, then the pit/tank may never get full throughout the building’s life span, especially for residential applications. 

The conventional system which places the backyard as the best position for sewer systems is now being countered by this contemporary approach which allows it to be built most conveniently in the front of the main building close to the perimeter fence and the public drain. It can be constructed such that a car can park over it without causing any problems. Using this system ensures a decentralized waste water treatment solution which is healthy to the users, the public and the environment. It is convenient, cheaper and easy to use and finally ensures that the septic tank never really fills up.   


  1. how often do you need to add the water treatment solution?

  2. As often as you want to empty it into the public drain. In most cases, users of this tech do this once a month.

    1. thanks means this system will not be possible for a house owner how does not live in the same compound where its constructed.

    2. It is possible only if the occupiers appreciate the concept and can follow up.