A typical septic system will need to be pumped every three to five years. This time frame varies depending on the size of the tank, and the amount and type of solids entering the tank. A septic tank needs to be pumped when the scum level is within 3 inches of the bottom of the outlet tee or baffle and when the top of the sludge layer is within 12 inches of the bottom of the outlet fitting. It is not necessary to use septic tank additives for your septic tank to function properly. Doing so can cause solids to carry over to the drainfield, which will result in early soil clotting. Such organic solvents can also pollute the groundwater.