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How do septic tanks work?

You’ve come to the right place if you want to learn about septic systems and how to care for them.

septic tank drawing

What is the purpose of your septic system?

A septic system collects and treats your household waste. A properly functioning septic system protects:

  • the health of your family and neighbors
  • the value of your property
  • the local water supply and environment

How does your septic tank work?

Your toilets, showers, laundry, sinks, dishwasher and garbage disposal all drain to your septic tank. There the waste settles into three layers:

  • Top layer - Soap, fats, oils and hair float to the top and form a layer of scum.
  • Middle layer - Water, with some suspended solids, is the largest layer.
  • Bottom layer - Sewage solids, food and foreign debris sink down and form sludge.

Beneficial bacteria are able to digest a small amount of the organic waste, but most of the solids stay in the tank in the form of sludge. Fats and oils do not get digested at all, and they stay as floating scum.

The water flows through to the second chamber of your septic tank. Any solids or scum still in the water should get trapped by the secondary chamber. Ideally the outlet of the septic tank has a filter that catches any particulates.

Only water should exit the septic tank. If any solids or scum flow out with the water, the particles will clog your absorption field.

In older tanks, inflowing waste simply pushes an equivalent amount of water out to the drain field. New systems are designed with a third compartment or dosing chamber, so that a specific amount of water is sent in doses to the drain field. If your septic tank is higher than your field, this is achieved with a dosing siphon. If your septic tank is lower, there is a pump to lift the water to the field.

Does the cold climate affect your septic tank?

Yes, the organic matter does not decompose as quickly in cold climates because there is less bacterial action. The beneficial bacteria that live in septic tanks work best at 98° F. Warm water from your shower or dishwasher helps, but the average temperature of septic tanks around here is too low for efficient digestion. Sludge builds up faster, which means septic tanks need to be pumped more often.

How does your absorption field work?

The septic tank removes all the solids, so that only water enters your absorption field (also called a leach field or drain field). A distribution box (D-box) divides the water equally among several trenches that have perforated pipes or chambers. These pipes run through a long bed of gravel or sand that is 2 to 3 feet below ground level. Some systems use a mound above ground level.

The water leaches or drains into the ground, where it is naturally filtered and purified. Some of the water evaporates, some is taken up by plants, and some percolates down to the aquifer.

Why is it important to maintain your septic system?

A septic system should last about 25 years. However, many systems fail prematurely due to neglect. Replacing a leach field can cost $10,000-$30,000. Regular pumping of your septic tank is one of the most important things you can do to protect your leach field. If your septic tank becomes too full of sludge or scum, solid particles will escape to your field. These particles will clog your field, and the water won’t be able to drain.

septic tank drawing

Does your tank have a dosing siphon or pump?

Septic systems installed in Summit County after 1985 will have a dosing chamber. This might be a third section of the tank, or a completely separate tank. If the dosing chamber is higher in elevation than your field, it will use a siphon to send doses of water to the field. If it is lower in elevation, you will have a pump to lift the water to the field.

Fields designed for use with a dosing system are smaller than older fields. If your dosing siphon or pump is not working correctly, it can cause the field to fail prematurely. Ideally the siphon or pump should be tested yearly, but at least have it done every few years when the septic tank is pumped. If the dosing siphon was correctly installed, it is usually trouble-free. Lift station pumps have a life span of 2-10 years, depending on the pump quality and usage. For more details, visit our Lift Stations and Pumps page.

Septic system dos and don’ts

A septic system should last about 25 years. However, many systems fail prematurely due to neglect. Replacing a leach field can cost $10,000-$30,000. Regular pumping of your septic tank is one of the most important things you can do to protect your leach field. If your septic tank becomes too full of sludge or scum, solid particles will escape to your field. These particles will clog your field, and the water won’t be able to drain.

  • Do pump your septic tank every 2-4 years
  • Do locate ALL of your septic system lids and keep them accessible, yet secure.
  • Do keep your tank fittings, including siphon or pump, in working order.
  • Do repair any dripping faucets or leaking toilets, which overload your septic tank.
  • Do use water-saving appliances, toilets and shower heads.
  • Do a little laundry every day instead of lots of loads in one day.
  • Do use lint filters and sink strainers.
  • Do limit the use of your garbage disposal, or pump your tank twice as often.
  • Do limit the use of bleach and anti-bacterial hand soap or detergent. These will hurt the beneficial bacteria in your septic tank.
  • Do plant grass or small plants over your leach field.
  • Don’t put sanitary napkins, tampons, paper towels, condoms, diapers, wipes, facial tissues, cigarette butts, or excessive toilet paper down the toilet.
  • Don’t put oil, fats or grease down the sink.
  • Don’t put paint, photographic solutions or other hazardous chemicals down the drain.
  • Don’t add bacteria, enzymes, yeast or other products. They aren’t necessary and may increase the amount of suspended particles entering your leach field.
  • Don’t allow trees or shrubs to grow on your field.
  • Don’t allow vehicles, large animals or anything heavy on your field.
  • Don’t allow hot tubs, rain gutters or surface water to drain into your septic tank.
  • Don’t pile up snow on your leach field.

How often should your septic tank be pumped?

About every 3 years is a good rule of thumb. It depends on the size of your tank, the number of people using the house, and how much food, fat, plastics and paper are put down the drain. Septic tanks in our area build up sludge faster and need to be pumped more frequently than tanks in warmer climates.

Can the sludge be measured to determine a pumping schedule?

Yes. The tank should be pumped when the sludge and scum together reach 1/3 of the liquid capacity. You can determine the sludge thickness by using a long stick wrapped with a white towel, similar to measuring the oil in a car. Remove the lid over the primary chamber of the septic tank (the lid closest to the house). Poke a hole in the scum layer, and lower the stick to the bottom of the tank. Let it sit a few minutes, and then pull the stick straight up. The black area on the towel is the sludge depth, and it should measure no more than a third of the total wet area of the towel.

If this process does not appeal to you, have the tank pumped every 2-3 years to be safe. The pumper should report the sludge and scum thickness, and you can adjust your pumping schedule accordingly.

How often should the filter be cleaned?

In Summit County, tanks installed after June, 2000 are required to have an effluent filter. This is a plastic mesh tube or brush that fits in the outlet tee of the secondary chamber. The filter catches anything that might otherwise clog up your absorption field. They are very good to have, as they will prolong the life of your field. However, they do need periodic cleaning, as a clogged filter can cause sewage to back up into your house.

Ideally the filter should be cleaned twice a year. If you only do it once, choose autumn, so you can get through the winter without problems. Remove the second septic tank lid, and pull the handle of the filter towards you. Rinse it off with a garden hose, being sure that the septage falls back into the septic tank. It is not necessary to scrub the filter spotless.

Where can you get more information?

Summit County Environmental Health Department The available brochure titled “Operation and Maintenance Manual” has very detailed septic system information.

Park County Environmental Health Department Click on “Helpful Information and Guidelines” to find an easy-to-read brochure on septic systems titled “Seven Homeowner Responsibilities”.

Eagle County Environmental Health Department

National Small Flows Clearinghouse, funded by the Environmental Protection Agency. Under Resources, click on “Products” to find septic tank brochures.

Clearwater Cleanup Company provides complete septic system care. Learn about our septic services.

Get the best septic care possible. We’ll clean your tank to the bottom, no matter how large or complex.