Excess waste water (rainwater gullies) volume entering the tank can result in the waste not having enough time to break down and disperse into the surrounding ground. This in turn would create a backlog within the septic tank and possible flooding or land pollution.
A lack of maintenance can cause a build-up of sludge within the septic tank. However, it is important to bear in mind that excessive emptying can also have a negative effect on the bacteria in the tank. This effectively prevents the bacteria from establishing themselves within the septic tank, therefore reducing the rate at which they can decompose the waste.
Incorrectly installed septic tanks result in the waste not being able to soak away or the sewage (including the solids) being short circuited into the soakaway system where they would cause detrimental blockages.
Collapsed baffles (which prevent the solids waste leaving the main tank) can result in any floating waste being transferred, harmfully, into the soakaway system. Collapsed baffles within septic tanks are often caused by incorrect emptying of the tank.