Sewage enters the primary chamber of the septic tank, where solids settle at the bottom via gravity. The settled solids are anaerobically treated reducing the overall volume within the tank. The liquid waste then flows through the dividing wall into the second chamber where further settlement takes place. The liquid is then discharged into a soakaway or if necessary, lifted to a sewage treatment system for further treatment before being discharged.
Waste will always remain in a septic tank despite the best efforts of anaerobic digestion as it offers very little treatment to settled sludge. The septic tank will eventually have to be emptied so as to prevent the sewage from overflowing into the drainage field (soakaway etc). This is not only very bad for the environment, but it will decrease the porosity of the soil and often clog up the soak way causing the raw sewage to back up and result in costly repairs being needed.
How often will I have to empty my septic tank?
This is determined purely by the volume of the tank in relation to the amount of solids going into it, the surface area contact and also the ambient temperature, as anaerobic treatment is more effective at a higher temperature. The emptying interval can vary greatly and often depends on usage, the diligence of the owner and also the different characteristics of each system. Some septic tanks need de-sludging every 4-6 months while others can go for over 12 months before requiring emptying. There is no set period of time determining how often a septic tank should be emptied.