How Septic Systems Work
A comprehensive guide to understanding your septic system, how it works, and what you need to know as a homeowner.
What is a Septic System?
A septic system is an underground wastewater treatment system used in areas without centralized sewer systems. About 20% of American homes use septic systems, primarily in rural and suburban areas.
Unlike municipal sewer systems that transport wastewater to a central treatment plant, septic systems treat and dispose of household wastewater on-site. When properly designed, installed, and maintained, septic systems effectively treat wastewater and protect public health and the environment.
System Components
House Plumbing
All drains in your home connect to a single pipe that leads to the septic tank. This includes toilets, sinks, showers, washing machines, and dishwashers.
Septic Tank
A watertight concrete, fiberglass, or plastic container buried underground. Solids settle to the bottom (sludge), oils float to top (scum), and liquid effluent flows out.
Distribution Box
Receives effluent from tank and distributes it evenly to drainfield trenches. Ensures all parts of the drainfield receive equal wastewater amounts.
Drainfield
Perforated pipes in gravel-filled trenches distribute effluent into soil. Natural bacteria in soil provide final treatment before water reaches groundwater.
How Your Septic System Works
Wastewater Enters Tank
All water from your home flows into the septic tank through the inlet pipe. Heavy solids sink to the bottom forming sludge, while lighter materials like grease float to form a scum layer.
Bacterial Breakdown
Naturally occurring bacteria begin breaking down the solid waste in the tank. This anaerobic process reduces solids volume by up to 50% and helps separate liquids from solids.
Effluent Discharge
The liquid layer (effluent) between sludge and scum flows out through the outlet pipe to the distribution box. Baffles prevent solids and scum from exiting the tank.
Drainfield Treatment
Effluent is distributed through perforated pipes into gravel trenches. As it slowly percolates through soil, aerobic bacteria provide final treatment, removing harmful pathogens.
Groundwater Recharge
Fully treated water eventually reaches the groundwater table. A properly functioning system removes over 90% of contaminants before water returns to the natural water cycle.
Types of Septic Systems
Conventional Gravity System
Most common type. Uses gravity to move effluent from tank to drainfield. Requires adequate slope and suitable soil.
Pump (Pressure) System
Uses a pump to move effluent when gravity flow isn't possible. Common when drainfield is uphill from tank.
Mound System
Drainfield is built above natural ground level. Used when high water table or shallow bedrock prevents conventional systems.
Aerobic Treatment Unit (ATU)
Uses oxygen to enhance bacterial treatment. Produces higher-quality effluent for sites with poor soil conditions.
Do's
✓Pump your tank every 3-5 years
✓Conserve water to reduce system load
✓Keep accurate records of pumping and maintenance
✓Know the location of your tank and drainfield
✓Direct roof drains and surface water away from drainfield
✓Use septic-safe toilet paper
✓Report any signs of system problems immediately
✓Have tank inspected when pumped
Don'ts
✗Flush non-biodegradable items (wipes, diapers, etc.)
✗Pour grease, oil, or fat down drains
✗Use excessive household chemicals
✗Park vehicles or build structures over drainfield
✗Plant trees or shrubs near drainfield
✗Connect basement sump pumps to septic system
✗Use garbage disposals excessively
✗Ignore warning signs of system problems
Key Facts About Septic Systems
21 Million+
Homes in the US with septic systems
25-40 Years
Average lifespan with proper maintenance
90%+
Contaminants removed by properly functioning system
Ready to learn how to maintain your system?