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Thursday, January 21, 2010

Pre-cast Septic Tanks

Almost 99% of homes in Kerala use septic tanks as a means of solid-waste disposal, unlike more developed economies that have centralized waste disposal systems. Until very recently, septic tanks were built on site using laterite blocks, brick or concrete, which accounted for high labour and material costs and were also not waterproof, which often led to ground water pollution; especially in water-logged areas. It is due to this mode of Septic Tank construction that Kerala Building Rules stipulate a minimum distance between the Septic Tank and the Well.

What is a Septic Tank?
A Septic Tank is a water-tight chamber into which faecal waste from toilets are deposited by means of sanitary pipes, which is then decomposed by bacterial action. An overflow pipe is provided from the Septic Tank to a Soak Pit to remove excess water so that undue pressure is not formed within the Septic Tank. A vent pipe is also provided to release methane and other gases that form within the chamber due to bacterial action.

Pre-cast Septic Tanks
Pre-cast Septic Tanks are manufactured in a factory and transported to the site for installation, thereby reducing Installation time and cost considerably. Moreover, the quality of the Septic Tank is also better than Cast-in-situ Septic Tanks as they are manufactured in Controlled environments in the factory, thus ensuring water-tightness and material consistency.
Pre-cast Septic Tanks are usually made of Polyethylene or Concrete. They have multiple chambers within them and a manhole for future maintenance. They have a diameter of about 1m and a length of about 2.5m depending on the number of water-closets attached to them.

Points to note during installation
1. Make sure that the manhole is on top while lowering the Septic Tank into the dug area.
2. Fill the Septic Tank with water completely before fixing the Sanitary Pipes, as a precaution against future settlement due to filled-weight.
3. Make sure that there are no stones, gravel or sharp objects below the Poly-ethylene septic tank. Place it on smooth earth.
4. An overflow pipe from the septic tank is to be connected to a Soak Pit, which should be able to let the excess water absorb into the soil. Do not locate the Soak Pit close to the well or any other fresh water source.
5. If the Septic Tank has not been used for a while, fill it up with water by pouring it through the water closet.
6. Avoid spilling soap, shampoo, phenol etc. into the water closet as this may kill the bacteria in the Septic Tank and prevent decomposition.
7. Vent-pipe should be raised high from the ground so as to prevent foul smell at normal habitable height.
8. A bit of diluted cowdung is advisable to be poured in the Septic Tank initially to activate bacterial decomposition.
9. Heavy objects or Heating should be avoided over Polyethylene Septic Tanks.
10. Use minimal water during flushing for better bacterial decomposition
More links on Pre-cast Septic Tank-


  1. It is a very good idea and this idea should reach to the all people. Everybody eager to know the cost and hopfully it will not be much high as everybody can reach

  2. It seems very promising to hear this type of septic tank, I would like to know more about the cost and how to get delivered to the work site if its out of kerala,

  3. The article is very informative.What should be the distance between the soak pit and fresh water well?