Pump Supply Lines: To Drain or Not to Drain?

Pump Supply Lines: To Drain or Not to Drain?

The answer to whether you need to drain pump supply lines depends on where you live. If you live in an area that does not typically have frozen ground, the use of a check valve is common. A check valve is included in the discharge assembly to prevent drainback through the pump after a dosing event. Drainback through the pump may cause bearings to wear out more quickly, shortening pump life. This would typically be an issue if the pump was turning on while drainback is occurring (which is not common). In this case, a vent hole (air release) must be provided between the pump and the check valve to prevent air lock of the pump.

In discharge assemblies for colder areas, a weep hole may be added to empty the piping and prevent freezing and limit the backflow through the pump. Typically, some of the effluent will also drain back through the pump and generally is not an issue unless the pump turns on during drainback. 

Be sure the pipe is well supported and bedded to prevent a bow from forming and draining back to the tank. The weep hole is typically 1⁄4-inch perforation drilled on the bottom of the pipe in the discharge assembly to assure that the supply pipe will drain. The other option is burying the supply line beneath frost depths.

Pumping downhill?

If the discharge point is at an elevation lower than the pump-off elevation, an anti-siphon device must be provided. Methods to implement an anti-siphon device include the following:

  • A drain hole used to allow drainback to the tank can also serve as an anti-siphon device.
  • A check valve installed in a reversed orientation at the highest point in the discharge pipe. When the pump activates, the valve closes. When the pump deactivates, the valve opens and breaks the siphon.  
  • A "spit tube" installed at the highest point in the assembly. The open tube breaks the siphon when the pump deactivates. A spit tube may also serve as a sampling port.

About the author
Sara Heger, Ph.D., is a researcher and educator in the Onsite Sewage Treatment Program in the Water Resources Center at the University of Minnesota, where she also earned her degrees in agricultural and biosystems engineering and water resource science. She presents at many local and national training events regarding the design, installation and management of septic systems and related research. Heger is the President of the National Onsite Wastewater Recycling Association and she serves on the NSF International Committee on Wastewater Treatment Systems. Ask Heger questions about septic system design, installation, maintenance and operation by sending an email to kim.peterson@colepublishing.com.


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