Preparing Seasonal Septic Systems and Cabins for Winter

Closing 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.

Winterizing the Pipes in the Cabin 

  • 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, leave faucets open. Completely drain the pressure tank. Flush toilets and add RV antifreeze to the tanks at the recommended dilution ratio. Check 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, drain 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, re-connect 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. Re-route 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, which 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 leaving the furnace on, it is a wise idea to conserve energy by installing a low-heat thermostat that will maintain the cabin at 40 degrees. 

Cleaning/Pumping The Septic Tank

Consider pumping the tank if closing the cabin 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. 

Vegetative Cover 

Stop cutting the grass over the soil treatment area in mid-September. The extra grass length will help capture snow, providing insulation over area. This can help prevent freezing.

Protect the Soil Treatment Area 

Keep all foot and vehicle traffic off the tank, pipes and soil treatment area (drainfield or mound). The only exception is the lawn mower. Do not plow snow off the area or store plowed snow over the drainfield.

Seasonal Care