Preparing Seasonal Septic Systems for Winter

Precautions taken in the fall can help prevent a frozen system — and avoid any surprises in the spring

Preparing Seasonal Septic Systems for Winter

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In cold climates, many residences are seasonal. Shutting down a septic system for the winter is a vital task for seasonal homeowners to prolong the life of the system and to keep it operating at peak performance. Precautions taken in the fall can help prevent a frozen system. Here are tips to help your seasonal customers close up their septic system.

Remind homeowners that these winterizing tasks will help them avoid any surprises in the spring. It’s also a good time for an inspection if the system is due for one, to make sure it’s functioning properly before the home is closed up for the winter.  

Winterizing the pipes

  • Do not add automotive antifreeze, salts or any other additives to your plumbing. 
  • If you leave the water on for the winter, be very sure that there are no leaks or drips. This constant, low flow of water can cause septic system freezing. This is common with high-efficiency furnaces. 

Even if the heat is left on, it is a good idea to drain water supply lines. Shut off the water where it enters the house and drain all lines. Drain the pump and then run a couple of seconds to be sure all water is out of the lines. Drain the system by opening all the faucets and leave them open. Completely drain the pressure tank. Flush toilets and add RV antifreeze to the tanks at the recommended dilution ratio. Check any flexible hoses in sinks and bathtubs to be sure they are drained completely. Remove and drain inlet hoses for the dishwasher and clothes washer. Clear the water valve by starting the machine for a few seconds, then drain the tub. Remove the drain hoses, and drain them completely. Disconnect the electrical supply to the pump, water heater, softener, washer and dishwasher. Drain the water heater and water softener with a hose after power is disconnected. RV antifreeze can be added to traps in sinks, bathtub and shower drains, washtubs, floor drains and sump pumps. In the spring, reconnect all hoses and flush the lines out before using again.   


If you have a high-efficiency furnace that is left on for the winter, be sure there is no water drip into your system. Freezing can result. Reroute the drip water to a floor drain, bucket or other source that does not enter the septic system at all, or enters in larger amounts. This water does not harm the septic system, but entering in very small amounts causes a trickle of water that can freeze more easily. If shutting off the furnace, drain all water from forced hot water and steam systems unless the system contains antifreeze. If that is the case, call a plumber for assistance. If the homeowner is leaving the furnace on, recommend that they conserve energy by installing a low-heat thermostat that will maintain the cabin at 40 to 50 degrees. It is also wise to open the doors of cabinets that have pipes in them so heat can get in. Pipes can also be insulated or wrapped with heat tape.

Septic system maintenance and pumping

Consider pumping the tank if the cabin will be closed for the winter, or if it will only be used a few times during the winter. If you live in an area with a high water table, you should only pump out the tank if the tank was designed for high water table conditions. If a tank is left full but the system is not used for the winter months, the sewage will get very cold and can even freeze. If the cabin is opened before temperatures in the soil start to rise, the effluent leaving the tank will be cold. By starting with an empty tank, you can then start fresh with warm effluent, which is desirable in the soil treatment area. 

If you have an aerobic treatment unit the blower should be shut off if you will not be using the system. Follow any other manufacturer requirements.

Protect the soil treatment area

Advise homeowners to stop cutting the grass over the soil treatment area in mid-September or so. The extra grass length will help capture snow, providing insulation over the area. This can help prevent freezing. To help prevent septic systems from freezing, spread a layer of straw or leaves over the system to provide insulation.

Remind homeowners to keep all foot and vehicle traffic off the tank, pipes and soil treatment area (drainfield or mound). The only exception is the lawn mower. Snow should not be plowed off the area and plowed snow shouldn’t be piled up over the drainfield.

About the author: Sara Heger, Ph.D., is an engineer, researcher and instructor in the Onsite Sewage Treatment Program in the Water Resources Center at the University of Minnesota. She presents at many local and national training events regarding the design, installation, and management of septic systems and related research. Heger is education chair of the Minnesota Onsite Wastewater Association and the National Onsite Wastewater Recycling Association, and she serves on the NSF International Committee on Wastewater Treatment Systems. Ask Heger questions about septic system maintenance and operation by sending an email to


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