|See also the Septic tanks category.|
for subtopics, how-tos, project pages, designs, organization pages and more.
A basic approach
Take a big concrete box, bury it in the back yard, run all your toilets and sink drain lines into the front of it, stick a few hundred feet of perforated drain pipe in shallow channels filled with gravel. Cover everything over with topsoil and forget about it. If you really want to you can dump some special 'septic tank bacteria' in it once in a while, or have it pumped out once a year. Most people ignore it - at least until it stops working.
Then you have to pump it all out, possibly even dig up the whole system and replace the field pipe, the tank, the lines, or everything. It is not exactly high technology, and it requires a bit of room (you couldn't have 60 septic fields for sixty houses in a 20 acre subdivision). You can't put them in where the water table is too close to the surface, or too near a stream/pond. I wouldn't call it wasteful. Some would like to make use of the methane generated, or the heat, or the composted solids. Others are happy enough to see it not get dumped into the local ground water.
In the developed world, this technology is mainly used where in remote areas; in poorer communities in the developing world, some form of septic tank may be the standard, even in high density settlements.
- The outlet should be considered a source of contamination, even though it should be less dangerous and unpleasant than raw sewage. The possibility of leaks must also be considered. Thus the tank and its discharge should be kept a safe distance from any water source ( perhaps 10 m is adequate[verification needed]).
- The application of a septic tank to a single house leads to relatively high maintenance, a high rate of problems, and greater cost. Sharing a septic tank between a number of houses (where those houses are close) may improve this, provided an effective approach to sharing the maintenance responsibility is found (e.g. sharing costs for a reliable contractor; or giving responsibility to the lowest level of government, if this design is commonly used in an area).
- Sharing a septic tank between a larger number of residences should make it more cost-effective to consider options such as more efficient designs and using the tank to produce biogas.
- DO NOT USE ANTISEPTICS! Antiseptics must NEVER be used in any toilet or drain leading to the septic tank, as they will kill the anaerobic bacteria, preventing decomposition, and leading to very unpleasant smells and an unsafe discharge.
- Do not allow the sediment to build up too much, as this will greatly reduce efficiency, increasing the odor, and the level of contamination in the outlet. UK Building Regulations Section H2 recommend an annual emptying interval.
- Do not allow any rainwater from guttering, yard drains, etc. to enter the septic system. This increases the hydraulic flow rate and flushes excess solids into the drainfield, which can be ruined as a result.
- Do not use any strong drain cleaners, caustic soda or similar products to clean the drains. These will kill the beneficial anerobic bacteria in the septic tank.
Septic tanks in the developing world
In Indonesia, the term septic tank - tenki septik - is used to describe a very standard method of sewage disposal, which is more basic than the septic tank used in developed countries. It is simply a ring of concrete, in a hole, with an unsealed (i.e. earth) bottom. Thus raw sewage is in direct contact with the earth. Where groundwater comes near the surface (for example Surabaya in East Java) this contributes to serious water contamination problems.