Why do I need to clean my septic tank every three years?

Beth Clawson<Clawsonb@msu.edu> - June 25, 2018

Regularly pumping and inspecting your septic system can help to keep your onsite wastewater system running longer, avoid costly repairs and protect water quality.

This diagram shows the basic construction and operation of a single cell septic tank. If the depth of the sludge layer or scum layer reaches the outlet pipes solids will fill plug the soil causing absorption failure. Keeping the sludge pumped regularly can prevent failure and increase the life of your onsite waste water treatment system. Graphic by Beth Clawson, MSU Extension.

Michigan is home to more than 1.3 million onsite wastewater treatment systems. Most are for single family homes that include a septic system. Indeed, the onsite wastewater treatment system including a septic tank and soil absorption field is the most common domestic wastewater treatment system in rural homes in the United States. In Michigan, it is estimated that 10 percent of these systems are in some level of malfunction or have failed.

Malfunctioning and failed onsite waste water systems make our ground and surface waters susceptible to fecal contamination. Several rivers in the Lower Peninsula have been tested during low-flow conditions and were found to contain genetic markers indicating the presence of human fecal matter. This contamination can come from leaky septic systems. Keeping septic systems in good repair can protect Michigan’s water quality.

Rural homes in Michigan include onsite wastewater systems that require regular maintenance. Maintenance and inspection of your system depends upon its size, the number of people that live in the home and what county you live in. Michigan is the last state to still adopt uniform onsite wastewater regulations. Lack of uniform statewide laws leaves regulation and inspection laws up to local officials through county health departments and districts. This means that rules for onside wastewater system laws vary between counties.

Most counties have a sale transfer ordinance requiring septic tank inspections but few have the same or similar size and installation regulations. Most ordinances cite the average of pumping and inspecting recommendation of every three years for a family of four. Many also require inspection of newly installed systems. None return a year or two later to ensure that the system is functioning properly.

An onsite wastewater system typically consists of three basic parts:

The drain waste pipes from the house into a septic tank;
The septic or settling tank, sometimes divided in half with a baffle; and
The dispersion box and soil absorption or drain field.

Waste water flows from the toilets, laundry and sinks in the home through the drain pipes to the septic tank. The septic tank, made of solid cast concrete (in most cases) has an inlet and an outlet for effluent. Once the waste enters the tank the solids settle to the bottom to decompose and become the sludge layer. Effluent water is in the middle and the lighter grease and soaps float to the top to create the scum layer. The effluent water flows out through a pipe to the drain field. Newer tanks sometimes contain a baffle creating a second settling area before water is released to the soil absorption field. Michigan State University Extension’s webpage on Septic systems gives more detail on this topic.

If the sludge is not pumped out on a regular basis then the layer gets thick allowing solids to flow into the drain field. This plugs and compacts in the drain tiles and the soil causing failure. Many times people think that this is a sign that the septic is full, and indeed it is but it is also a failure. Drain field failure requires soil removal and replacement and can become an expensive repair. This is one of the most common failures. Other common causes of septic failure include tanks collapsing from being driven or parked on; tree roots; excessive water from parties or heavy rains; pipes clogged from flushing items other than toilet paper such as, feminine products and personal sanitary wipes; biological processes stopped from over use of chlorine or antibiotic soaps.

If you are experiencing sewage waste backup into your house from your septic tank this may indicate a total blockage of the tank and drain field and could indicate a costly repair or replacement. Regular inspections and pumping can prevent expensive repairs later. Just as it is recommended to regularly inspect our cars and furnaces, we should also inspect and clean out our onsite waste water systems. The average recommendation is every three years for a typical family home with three bedrooms equipped with a 1000 gallon tank. It's important to know the size of your septic tank.

Older homes may have smaller tanks. Smaller tanks need to be pumped more often. For example, if a three-bedroom home has a 900-gallon septic tank with six people living there, they should schedule their pumping for every one and one half to two years to avoid failure. If a home uses a garbage disposal consider that they are increasing the amount of solids (pre-digestion) going into the tank. This home will require more frequent pumping.

Concrete, plastic and fiberglass tanks are not infallible, lots of things can cause the material to fail resulting in collapse. Inspectors look at the integrity of your system. Fractures caused by frost/freeze break up, ground heaves, earthquakes, manufacturer defect, burrowing animals, and tree roots all have an impact on our systems. Michigan DEQ does have a guide on subsurface onsite wastewater treatment systems but its recommendations are not enforceable by law. Michigan County Environmental Health departments have laws, consult your County for its recommendations for onsite waste water system maintenance.

For more in depth information the National Environmental Services Center, West Virginia University has a good publication that includes a time table in years for pumping recommendations at http://www.nesc.wvu.edu/pdf/ww/septic/pl_fall04.pdf.

If you want to learn more there are videos available: Click here for a short video (under five minutes) about onsite wastewater septic systems, or click here for a longer training video (about 110 minutes) about onsite wastewater septic systems.

For more information about and water quality contact Beth Clawson, MSU Extension Educator. To learn more about onsite waste water treatment septic tanks, contact Michigan State University Extension Natural Resources educators who are working across Michigan to provide water quality and septic tank maintenance educational programming and assistance. You can contact an educator through MSU Extension’s “Find an Expert” search tool using the keywords “Natural Resources Water Quality.”