Ask the Builder: Demystifying septic systems

Are you wondering how septic systems work? I never thought about it much in all the years I’ve lived in Cincinnati. Every house I lived in was connected to a city sewer. I have connected almost every house that I have built to a sewer system. Some of the houses I’ve built needed their own sewage treatment plants.

However, such a house catches my eye. The property was not large enough to support a traditional leach field. (I’ll go into what a lye field does in a moment.) It required a sewage treatment plant that was essentially a miniature treatment plant.

There was a propeller on one shaft that reached into the septic tank. It was attached to a weatherproof engine. This motor turned for 10 minutes per hour and worked like a kitchen mixer. As the propeller turned, fresh air was also blown from outside into the swirling mass of water and waste in the septic tank.

Visit a medium or large sewage treatment plant and this is what you will discover. Before it directs the wastewater back into the nearest river, the system aerates the wastewater. Introducing oxygen into sewage is a fantastic way to get rid of all of the harmful things that could be found in sewage.

If you are unfamiliar with how septic systems work, here is an introduction. When you flush your toilet, or when water drains from a bathtub, shower, vanity, or kitchen sink, the sewage flows through a 4-inch pipe connected to a large prefabricated concrete tank.

The capacity of the tank can range from 500 to 1,000 gallons or more. They are sized by septic designers based on the projected amount of waste that could be generated in the house each day. Typically, the designer goes by the number of bedrooms in the house.

Some tanks have different walls and baffles within the tank. The ones I see most often in New Hampshire have a small wall about a foot from where the house drain pipe goes into the tank.

The purpose of this concrete suspended wall is to break down solids and toilet paper that goes into the tank. These things are supposed to crash into this wall when they enter the tank.

The problem is that in most tanks there are inlets that allow the plumber to install the drain pipe parallel to that wall. Make sure your tank is installed properly so that the drain pipe goes into the tank and is facing that little wall.

The wastes from your body, foods, and oils from your skin all contain bacteria. These bacteria start to work in the tank to break down the waste.

At the other end of the tank opposite the inlet pipe is an outlet pipe. For every gallon of water that goes into the septic tank, one gallon of water flows out of it. This partially treated water that leaves the tank contains many microscopic bacteria and pathogens.

It flows from the tank or is pumped up a hill to the leach field. The wastewater enters a labyrinth of pipes with perforations. The pipes are typically laid on a thick layer of washed sand. The wastewater is distributed to several pipes, where it then slowly ends up in the sand.

There is a lot of oxygen and small organisms in the sand. These work together to purify the wastewater that drips from the lye field pipes. It’s a simple system that has proven itself. The best part is that if you pay attention to what you put in your septic tank, it works very well.

Years ago when I lived in Cincinnati, I threw everything I could down my drainpipe. Unfortunately, I felt like it wasn’t my problem as long as it went down to the sewer. That was a bad attitude, and city sewer operators wish more people would take care of it. For example, I would clean my brushes in a sink and not kid myself. I would emulsify fat from kitchen pots and pans and it no doubt froze further down the sewer.

You never want to put any of these things or chlorine bleach or chemicals in a septic tank. The only thing that should go in the tank is waste from your body and toilet paper. The cheaper the toilet paper, the better. Never put flushable wipes in a septic tank or municipal sewer system. Why? Go to and watch my video on flushable wipes.

If you are planning to build in a rural area that has a septic tank in your future, install a sink in the laundry room or garage that drains directly to the outside. In other words, don’t connect the sink to the septic tank.

Many inspectors let this gray water flow away from your house to the floor because they don’t want you to dump paint, grease, or who-knows-what into your septic tank. Wash all the bad things in this sink, not the other sinks in your home.

It is important that you pump your septic tank at least every three years. It’s affordable and makes sure you don’t ruin your leach field. It can cost thousands of dollars to replace a lye field. I’ll only pay $ 285 in 2021 to pump out my 1,000 gallon septic tank. You can see why this is really worth doing. The average cost per year is less than $ 100.

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