Understanding Septic Systems

article image
Under most conditions, a septic tank will need to be pumped out by a professional every two to five years.

A septic system is the most common way to treat household wastewater if connections to a municipal sewer aren’t available where you live. But few people who rely on septic systems understand how they actually work. And without correct knowledge, you’re open to misinformation or accidental mismanagement that could cost you lots of money.

The word septic means “absence of oxygen” and that’s the state of affairs in the first part of every septic system — the tank. This is where raw sewage is broken down by anaerobic bacteria, liquefying most of the solids. Indigestible bits settle out into the bottom of the tank, a bacterial scum develops on the surface of the sewage, and excess liquid flows out of the tank into a network of perforated pipes buried underground. This area is large, and extends beyond the tank. It’s called a leaching bed, or weeping bed, and it’s the place where 90 percent of sewage purification occurs as nutrient-rich wastewater dribbles out of holes in the pipes. After this happens, soil microbes, insects and roots of grass purify the water. (Don’t plant vegetables in this area.)

Keep Things Flowing Smoothly

Septic systems can function for decades, as long as the soil around the perforated pipes remains porous enough to allow wastewater to drain away. But after the soil loses this porosity, sewage backs up and you’ll have a major problem.

Routine maintenance of your septic system is aimed at retaining the all-important porosity of the leaching bed, and this is the reason septic tanks need to be pumped out every two to five years by a professional (gases produced by a septic system can be deadly). Because the septic digestion of incoming waste is never complete, an indigestible sludge slowly builds up in the bottom of the tank. And while this is normal, it means the effective size of the tank is constantly getting smaller. If tank capacity is reduced enough, solids are forced out into the leaching pipes where they’ll clog the soil and ruin your system.

Few people realize how bad washing machine lint is for septic systems. The small particle size of lint means that it doesn’t settle to the bottom of the tank. If you’re washing machine filter allows enough lint to slip past, it’ll clog your leaching bed prematurely.

When the Water is Rising

The first thing to look at if your septic system goes bad is sewage loading immediately before the problem occurred. Did you have a lot of house guests? Have you been doing a lot of laundry? Backed up main drains or a swampy back yard might be caused by temporary overloading of the system. Limit water use for a few days and see what happens. If the problem remains, you could have a congested leaching bed, though not necessarily.

It’s possible the non-perforated distribution pipe connecting your septic tank to the perforated leaching pipes is blocked or has collapsed. Tree roots can block lines, too. I’ve also seen situations where the end of the incoming sewage pipe clogs just inside the septic tank because of the T-shaped pipe fittings that are often used in this location. Because of the dangers involved with sewer gases, these repairs are best left to professionals.

The oldest continuously operating septic system I’ve ever seen was built in 1969. But even a system that’s so obviously well-built will eventually fail as the leaching bed inevitably clogs. Digging out the soil and replacing it with new, sandy fill is one way to fix the problem, but there are less expensive alternatives that work in some cases. Something called “terra lifting” is a case in point. This procedure involves drilling holes in the leaching bed 4 to 6 feet apart, then blasting air and/or perlite balls into the soil to re-establish enough porosity to let wastewater drain away.

Don’t Be Duped

Whatever you do, don’t buy those ridiculous claims for septic system additives that promise to eliminate the need for pump-outs. No additive in the world can make the indigestible part of sewage completely digestible, and if you’re led to believe otherwise you could be setting yourself up for a smelly and expensive run-in with reality.

For more information, read The Truth About Septic Systems and Septic System Basics.

Have you experienced unusual septic system problems? Share your stories and solutions in the comments section below.

Contributing Editor Steve Maxwell has been helping people renovate, build and maintain their homes for more than two decades. “Canada’s Handiest Man” is an award-winning home improvement authority and woodworking expert. Contact him by visiting his website and the blog, Maxwell’s House. You also can follow him on Twitter, like him on Facebook and find him on .