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Cleaning (Pumping) Septic Tanks

Onsite wastewater treatment (septic) systems normally include two parts: a septic tank, the first component of the system, followed by a secondary wastewater treatment component, such as a soil absorption leach field. The septic tank acts as a settling chamber that allows wastewater to separate naturally into three distinct layers before liquid flows out of the tank. First, solid particles settle to the bottom of the tank to form a layer of sludge, where some of it is digested by anaerobic bacteria. Second, greases and fats float to the top of the wastewater in the tank and form a second layer, or scum layer. Third, a clearer layer of liquid wastewater develops in the middle--between the sludge layer at the bottom and the scum layer at the top of the wastewater in the tank. The liquid layer of wastewater eventually flows out of the tank to the secondary treatment component (usually the final treatment component) of the system.

A normally functioning septic tank provides primary treatment of wastewater, which includes the separation of wastewater into three layers and the partial digestion of sludge by anaerobic bacteria. With normal contributions of wastewater to the system, sludge continues to build up at the bottom of the septic tank over time, despite the anaerobic digestion of some solids. At the same time, the layer of scum on top of the wastewater continues to grow thicker. The continual growth of the two layers--the sludge at the bottom and the scum at the top--effectively reduces the storage capacity of the tank and shrinks the middle liquid layer of wastewater. As this happens, wastewater flows more rapidly through the tank, which means there is less time for the wastewater to settle out solids and separate scum from the liquid. Unless there is adequate space in the septic tank for wastewater to separate into layers, solids and scum will float out of the tank and into the secondary treatment component of the system. Eventually, the secondary treatment component will clog and the entire system will fail.

The Need for Regular Tank Pumping

To help ensure the proper maintenance and long term functioning of the entire onsite septic system, the septic tank should be pumped out every three to five years, given normal household water usage. Pumping the tank helps prevent sludge and scum from flowing out of the septic tank and into the secondary treatment system.

Proper tank cleaning refers only to removing all the solids and scum from the tank by pumping, not by any other means. Adding septic tank "additives" to the system is not a proper substitute for tank pumping and may actually harm the system if it causes solids to become suspended and flow into the secondary treatment component of the system. It is also not necessary to add bacterial additives to the septic tank after tank pumping, since there is sufficient bacteria present in normal household wastewater for proper functioning of the system.

Licensure of Tank Cleaners

Iowa Administrative Code (IAC) 567 Chapter 68, "Commercial Septic Tank Cleaners", requires septic tanks to be pumped out only by a licensed commercial septic tank cleaner, which is a person or firm licensed by the Iowa DNR to clean septic tanks. A list of licensed septic tank cleaners is provided below. Persons or firms interested in applying for a commercial license to pump septic tanks may complete the application form provided below.

List of Iowa Septic Tank Pumpers

[542-2010] Licensed Tank Pumper Application

Standards for Disposal of Septage

Disposal of wastes (septage) from private waste facilities (septic tanks) shall be carried out in accordance with the requirements of 567 IAC Chapter 68 (see link above).


The county boards of health are responsible for enforcing the standards and licensing requirements contained in Chapter 68 and other referenced rules relating to the cleaning of private waste facilities and disposal of waste from such facilities.

Recordkeeping Requirements

Commercial septic tank cleaners are required to maintain records of private waste facilities cleaned and the location and method of waste disposal. Such records shall be maintained for a period of three years, and shall be made readily available upon request to county board of health or department officials.

More Information

For more information on septic tank pumping, contact Tim Grotheer at or 515-452-7646.