Glossary

Definitions for some of the most common terms related to septic systems and grease traps are provided here.

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bacteria, friendly bacteria - Microorganisms that break down organic material in wastewater. Some bacteria are naturally occurring. You may add appropriate bacteria to the septic tank (by flushing down a toilet) every month.

drain field - See lateral, lateral field.

grease trap - A tank that “traps” grease from kitchen wastewater before it reaches the sewer system. Restaurants and other facilities that do lots of food preparation will have grease traps. Home septic systems rarely have grease traps. The purpose of a grease trap is to prevent the fats and other food waste from getting into the pipes to the sewer system laterals where they can cause clogging and system backup. Grease traps require frequent cleaning, according to local agency regulations. There are two basic types of commercial grease traps: an outdoor style with access via a manhole that typically holds 1,000 gallons, and a smaller, indoor type.

holding tank - A watertight container that collects the wastewater stream. When not part of a septic system, it is not designed to allow bacterial breakdown and the wastewater must be pumped out frequently.

lateral, lateral field, lateral system - A lateral is a branch of the underground piping that extends from the septic tank’s outlet. The wastewater continues to decompose and eventually filter into the soil through small holes in the laterals.

leach field - See lateral, lateral field.

septic tank - A watertight tank that collects wastewater from a home or other facility for treatment. Usually made of fiberglass or concrete and buried underground. A septic system requires bacteria to break down the wastes. Some bacteria is naturally occurring, but septic systems generally work best when bacteria is added to the tank. The normal water flow from sinks, toilets, washing machines, etc. carries the liquid from the tank out to the lateral field, while solids settle to the bottom of the tank. The solids that remain in the tank create a sludge that must be removed (pumped out) periodically. Septic tanks are sized according to the number of people living in the home or using the facility, as well as other features, such as garbage disposals.

sludge - The accumulated solids in the bottom of a septic tank. Sludge must be pumped out periodically (every three years for a typical family of four with a 1,200-gallon tank).

vent pipe - A pipe that vents “sewer gas” from toilets.