Troubleshooting: What Should the Service Provider See in the Tank?

Troubleshooting: What Should the Service Provider See in the Tank?
Jim Anderson

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When opening the septic tank, carefully inspect the lids and covers for any damage and structural integrity. If concrete lids are cracked or deteriorating, there may be other structural problems. It should be a red flag to pay close attention during the rest of the investigation. All parts of the tank need to be accessible to inspection. This means covers over both the inlet and outlet baffles need to be opened and inspected as well as any larger manholes or access points. Any damaged lids need to be noted and replaced or repaired so they are safe. Every year there are reports of people, often children, falling into tanks through defective lids and being seriously hurt or killed. 

If a septic tank is operating normally the liquid level should be at the invert of the outlet pipe. There should be three distinct layers in the tank — a floating scum mat, a clear zone, and the sludge or solids at the bottom. If these layers are not present, the bacterial action in the tank is not taking place the way it should. This could result in excessive solids in the soil treatment unit, causing plugging and excessive biomat development. 

Now that most states require an effluent screen at the outlet baffle, solids are captured rather than moved downstream to the drainfield. When the screen becomes plugged the liquid cannot move out of the tank and backs up. Depending on elevations and the location of the tank, the liquid can back up into the lower levels of the house or rise into the access risers and to the surface. 

There are several potential causes of the tank biology being affected — these can be explored with the homeowner. These include use of a water softener, use of excessive cleaning products containing bleach (which is chlorine and antibacterial) or other antibacterial cleaners and soaps, dumping toxic solvents and materials down the drains, and someone in the household using heart medication or on chemotherapy for cancer treatments. 

If it looks like the tank is operating correctly but excessive solids buildup has plugged the effluent screen, the homeowner should be consulted about their water use and system habits. Some of the common causes of solids plugging effluent screens prematurely include: 

  • Use of a garbage disposal (this increases solids and creates solids that are more difficult to break down)
  • Certain types of additional food preparation
  • Operating an in-home business (daycare, hair salon)
  • Presence of a sewage sump or large bathtubs on the second floor — both of which may stir the solids off the bottom of the tank 

The homeowner and service provider should come up with a plan to address any problems that are identified through discussions. 

There are homeowner surveys available to guide the service provider in determining whether water use and homeowner habits are part of the problem. Solutions are usually increased maintenance or inspection routines. Rather than being on a three-year schedule to inspect and clean the tank, the service provider can recommend at least evaluating the tank every six months to gauge where the solids production is and then come up with the appropriate maintenance schedule. Through these discussions and visits the service provider can better serve the homeowner, but also help them recognize they can impact the maintenance frequency by how they use the system and to adjust their schedules. 

Next up we will look at the inlet and outlet baffles along with tank water levels. 

About the Author
Jim Anderson is connected with the University of Minnesota onsite wastewater treatment education program, is an emeritus professor in the university’s Department of Soil Water and Climate, and education coordinator for the National Association of Wastewater Technicians. Send him questions about septic system maintenance and operation by email to


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