Septic Systems: How They Work and How to Maintain Them

In most urban environments, when you flush the toilet, the waste is piped out to a sewage treatment plant. That plant treats and separates the waste into water that’s clean enough to be discharged into a river and into solids called residual waste. The residual waste gets landfilled or used as fertilizer.

In some areas where there aren’t sewage treatment plants, septic systems do largely the same thing, but on a much smaller scale. Waste-water leaves the house and empties into an underground septic tank that’s usually 20 to 50 feet away from the house, beginning the treatment process.

What are Septic Tanks and How Do They Work?

Septic tanks are made from concrete or heavyweight plastic and typically have a capacity of 1000 to 2000 gallons.

There are two chambers in the tank, separated by a partial wall. Waste flows from the house into the larger chamber. Solids settle to the bottom, and liquids make their way over the partial wall into the smaller second chamber. Naturally occurring anaerobic bacteria digest the solids, turning them into the water, carbon dioxide, and a small portion of indigestible material.

Septic Fields Distribute Liquid Effluent

There’s an outlet pipe in the second chamber through which the liquid (known as effluent) from the tank flows toward a disposal or leach field. There, the effluent drains into the ground through a series of perforated pipes or through perforated plastic structures called galleries. The pipe or the galleries are placed in a bed of gravel that helps disperse the liquid.

As the effluent percolates through it, the soil absorbs residual bacteria and particles so that by the time the water reaches the aquifer deeper underground, it’s pure enough to drink. Septic fields are usually just a foot or two below the surface to keep the effluent away from people and pets, but not much deeper because a significant amount of water escapes through evaporation or is transpired by grass growing above.

Septic fields require the right kind of soils. Sandy soils that drain too quickly may not treat the effluent well enough. In these cases, deep excavation is made prior to the field’s installation and is filled with an engineered soil that provides the necessary filtration.

In other cases, native soils with a high silt or clay content don’t drain well enough to dispose of the water. In those situations, mound systems are built, where engineered fill is placed on the native ground and the septic field goes into the top of the mound. The mound is covered with topsoil and seeded with grass, and more of the water escapes through transpiration and evaporation.

Septic Systems Rely on Gravity, Most of the Time

Most septic systems rely on gravity to move the liquid from the house to the tank to the field.

Sometimes though, the slope of the lot requires the tank or the field to be higher than the house. For that to work, a pump is needed, or sometimes two pumps.

If the tank is higher than the house, a grinder pump that liquefies solids will be placed in a pit in the home’s basement or crawlspace. If a pump is needed between the tank and the field, it will be in an underground pit accessed through a manhole on the lawn.

Sewage pumps are essentially heavy-duty sump pumps. When the effluent in the pit rises to a certain level, a float triggers a switch that turns on the pump and drains the pit.

How to Treat Your Septic System

For the most part, you don’t have to do anything to keep your septic system healthy except mow the grass above and keep the drainage area clear of trees and bushes whose roots can clog the field.

It’s important to be mindful of what you flush down the toilet—which shouldn’t be anything other than toilet paper and human waste. According to the Environmental Protection Agency, pouring toxins down the drain can kill the organisms in your septic system that digest and treat household waste. This could harm your septic system.

How Often Do You Need to Pump A Septic Tank?

About every two years, you should have a septic service pump the solids from the tank. Modern tanks will have a manhole at the surface for the pump operator to access, but older systems might require that the top of the tank be dug up to expose the pumping hatch.

If you don’t have it pumped regularly, the tank will fill with solids that will eventually make their way into the leach field and clog it. You’ll know this is happening because untreated effluent will make its way to the surface of the tank will back up into the house.

This can require the replacement of the entire field. Regular pumping of the tank can keep leach fields functioning indefinitely.

What to Do if Your Septic System Fails

As with any mechanical system, pumps in a pumped septic system will eventually fail. Most pumps are wired with an alarm that lets you know if the effluent level in the pit is higher than it should be, signaling a pump failure. This is a job for a professional.

To find a reputable list of installers and septic system service providers in your area, visit:

A well-maintained septic system is trouble-free and something a homeowner doesn’t have to think about much. Just keep the tank pumped and the lawn mowed and you should get decades of trouble-free service.

Are your home’s systems and appliances protected against unexpected repair needs? If not, consider investing in a home warranty.