Few of the houses I’ve built have needed their own septic systems. One house that did, however, stands out in my mind. The lot wasn’t big enough to support a traditional leach field. (I’ll get into what a leach field does in a moment.) It required a septic system that was, in essence, a miniature sewage treatment plant.

There was a propeller on a shaft that extended down into the septic tank. It was attached to a motor, and for 10 minutes an hour this motor would spin much like a kitchen blender. When the propeller spun around, fresh outdoor air entered the swirling mass of water and waste inside the septic tank.

Visit a sewage treatment plant and what you’ll discover is a similar design. Before it sends the sewage back into the closest river, the plant aerates the wastewater. Introducing oxygen to sewage is a fantastic way to get rid of harmful things that one might find there.

If you’re unfamiliar with how septic systems work, here’s a primer. When you flush your toilet or when water drains from a tub, shower, vanity or kitchen sink, the wastewater flows through a 4-inch pipe that connects to a large precast concrete tank. The capacity of the tank can range from 500 to 1,000 gallons, or more. Tanks are sized by septic designers based on the amount of projected waste generated within the house each day. Typically, the designer goes by the number of bedrooms in the house.

Some tanks feature different walls and baffles within the tank. The ones I see most often in New Hampshire have a small wall located about a foot from where the house’s drainpipe enters the tank. The purpose of this suspended concrete wall is to help break down any solids and toilet paper that rush into the tank, with waste products crashing against this wall as they enter the tank.

The trouble is that there are inlets into most tanks that allow the plumber to install the drainpipe parallel — rather than aimed at — this wall. Be sure your tank is installed correctly so the drainpipe enters the tank aimed directly at this small wall.


Waste from your body, food and oils from your skin all contain bacteria. This bacteria works in the tank to break down the waste. At the other end of the tank, opposite the inlet pipe, is an outlet pipe. For each gallon of water that enters the septic tank, a gallon of water exits it. This partially-treated water that leaves the tank contains microscopic bacteria and pathogens.

It flows from the tank, or is pumped up a hill, to a leach field. There, the wastewater enters a maze of perforated pipes. The pipes typically rest upon a thick layer of washed sand. The wastewater is distributed into multiple pipes where it then slowly enters the sand.

The sand contains oxygen, as well as numerous small organisms. These work in tandem to purify the wastewater as it drips out of the leach field pipes. It’s a simple system that’s time-tested. Best of all, it works well if you watch what you put in your septic tank.

Years ago, I put anything I could down my drainpipes. Foolishly, I felt that as long as it made it out to the sewer line, it wasn’t my problem. That was a bad attitude, and municipal sewer plant operators wish more people would care. For example, I’d clean paint brushes in a sink, thinking nothing of it. I’d emulsify grease from kitchen pots and pans, no doubt that it congealed farther down in the sewer.

You never want to put any of these things, or chlorine bleach or chemicals, into a septic tank. The only thing that should go into the tank is bodily waste and toilet paper. The cheaper the toilet paper, the better. Never put flushable wipes in a septic tank or city sewer system. (Why? Go to AsktheBuilder.com website and watch my flushable wipes video!)

If you plan to build in a rural area where a septic tank is necessary, install a utility sink in the laundry room or garage that drains directly outdoors. In other words, don’t connect this sink to the septic tank. Many inspectors allow this gray water to flow onto the ground away from your home because they don’t want you to put paint, grease, or who-knows-what into your septic tank. Wash the bad things in this sink, not the other sinks in your home.

It’s vital that you pump your septic tank at least every three years. It’s affordable and it ensures that you won’t ruin your leach field. It can cost thousands of dollars to replace a leach field. I only pay, in 2021 dollars, $285 to pump out my 1,000-gallon septic tank, meaning the average cost per year is less than $100.

Tim Carter has worked as a home improvement professional for more than 30 years. To submit a question or to learn more, visit AsktheBuilder.com.