Even with a healthy microbial ecosystem breaking down the septage, a well-functioning septic system and good drain field, the sludge and scum layers in your tank will build up over time. The sludge and scum should be pumped out periodically -- generally when the bottom of the floating scum layer is within 6 inches (15.2 centimeters) of the outlet pipe or the top of the sunken sludge layer is within 12 inches (30.4 centimeters) of it [source: EPA]. Without a well-developed power of extrasensory perception, it's impossible to tell when your waste has reached these levels.
This is why it's recommended that people with a septic tank have their system checked every year [source: Seattle-King County Public Health Department]. Having your system inspected includes getting your sludge and scum levels measured, checking the system's pipes and mechanisms and inspecting the drain field to make sure it's percolating the effluent properly. The average septic tank system usually requires pumping every one to three years [source: EPA].
There are some products on the market that are meant to prolong periods between pumping. These products contain chemicals designed to hasten the process of breaking down the sludge in your tank by acting like tiny Pac-Men chomping magic pellets. At the least, products such as these may be superfluous: The additives are simply joining the microbial party already in full swing below your lawn. In the worst case, the chemicals can throw the primordial ecosystem that's developed over time in your septic tank thoroughly out of whack and disrupt the natural enzymes' ability to properly break down the waste sent to it. The Environmental Protection Agency (EPA) recommends that septic tank users play it safe and not substitute these products for regular septic tank inspections and pumping [source: EPA].
Without regular pumping of the septic tank, the system can overflow. Sometimes overflow can lead back to the house, where toilets and drains belch forth what's supposed to be in the septic tank. Overflow can also lead to a sudden deluge of unprocessed waste flooding the drain field. When this happens, water can seep above ground, which leads to a flooded yard and run-off into nearby water bodies like creeks and rivers. Below ground, this flood can cause further damage, tainting groundwater. Together, these intrusions of waste can contaminate the water people use and drink. The waste introduced into the water supply can carry harmful bacteria and diseases like hepatitis [source: EPA].
But even after it's taken from your backyard, your septic tank's contents still pose a hazard. So what happens to it? Read the next page to find out.