A septic system is comprised of two primary components, the septic tank and the soil absorption field. The soil absorption field is typically connected to the septic tank by piping.

The septic tank removes solids from the waste water. Waste enters the septic tank through the inlet baffle. Solids remain in the septic tank and the waste water effluent exits the tank through the outlet baffle. Up to 50% of the solids that enter the tank decompose. The remaining solids accumulate in the tank. Through the decomposition stages, sludge is created and settles to the bottom of the septic tank.

A typical soil absorption field is a series of gravel lined trenches, each of which contains a 4 inch, perforated pipe. All waste that exits the septic tank is carried to the soil absorption field and dispersed through these pipes, where the liquid is absorbed into the soil.

As the septic system is used, sludge accumulates in the septic tank over time. When there is too much sludge in the septic tank, solids do not have enough time in the tank to settle, and they enter the soil absorption field.

Solids that enter the soil absorption field will eventually clog the perforated pipes. When the septic tank is full and no longer protecting the soil absorption field, it is only a matter of time before the soil absorption field fails.

To avoid this situation, the solids which remain in the septic tank must be pumped out periodically.

Many factors determine septic tank pumping frequency. Typically, when the septic system is designed, the size of the septic tank and the soil absorption field are determined based on the square footage of the dwelling, and the number of bedrooms it contains. These factors make assumptions regarding the number of occupants, and therefore the amount of waste that will be created and processed in the septic system.

These are only assumptions and the actual waste created can vary considerably from the benchmark figures. The actual number of occupants in the house can be more or less than used in the sizing calculations, and soil absorption rates can also impact septic pumping frequency. Activities such as the number of loads of laundry that are done, the frequency of running a dishwasher, and the presence of a garbage disposal (which is a big offender in depositing an abundance of unanticipated solids in the septic tank), all effect how often a septic tank needs to be pumped.