Thaw Frozen Septic Line

Thaw a Frozen Septic Line

After arriving at the cabin on a bitter January weekend last year, we found our drains were not working. The toilet would not flush, and the sinks would not drain. It didn’t take long to figure out what was going on. We had a frozen septic system.

Domestic septic systems work remarkably well, even in frigid climates. However, given the right conditions, septic lines and holding tanks can freeze.

What are those “right” conditions? Simple; cold and water.

Most septic systems avoid ice formation by the thermal protection offered by a buried system and the flushing and warming effects of routine use. Without these, systems can freeze.

In our case, our system was bound to fail. It was a very cold January with little snow cover. Our relatively shallow septic line, without the insulating benefits of snow, was almost certainly above the frost level and plenty cold to make ice.

In addition, we had not been at the cabin for some time, robbing the septic system of the beneficial warming and flushing effects of the home’s plumbing.

The system was cold; all it needed was water to form ice.

Our water source? The furnace. As it turns out, the condensate water from our furnace empties into the septic system. This continuous source of low-flow water added to our cold system readily filled our septic line with ice.

So, what could we have done to prevent this and how do we prevent it from happening again? The simple answer; keep the system warm and/or avoid introducing low-flow continuous water sources to the system.

Septic Systems Freeze For Many Reasons 

Risks factors for a frozen septic system – things that make it too cold

  • Septic line too shallow – line installed above or too close to frost level
  • Septic line below compacted soil (driveways, paths) – compacted soils tend to freeze deeper
  • Snow cover inadequate or compacted – loss of insulation effect of snow
  • Lack of vegetation or grass cover – vegetation acts as insulation for soil

Risks factors for a frozen septic system – things that allow ice to form

  • Infrequent use of system – use of system flushes pipes and adds heat to system
  • Constant low volume water source (furnace condensation drainage, leaking faucet) – provides water to create ice buildup without benefit of flushing system
  • Improperly pitched septic line or low spots in line travel – water cannot exit septic line completely allow it to freeze
Frozen septic line.

Frozen septic system line, showing ice formation in the septic line.

Septic systems can have many factors leading to ice formation. Each needs to be considered and addressed to prevent future freeze ups. But, before we can address the problems, we need to de-ice the frozen septic line and re-open the system.

But, before you can address the problems, you will obviously need to thaw any ice within your lines and re-open the system.

Your septic line is frozen, now what? Easy; thaw it out!

To fix a frozen septic, you will need to thaw the ice that is blocking the system or line.

I did this myself and you likely can too. Before jumping into this, seriously consider calling a professional who specializes in clearing frozen septic systems. The first time my system froze, I did just that. For $250 the problem was fixed in 15 minutes.

Like most things in life, this project is a question of risk vs. reward. If you like the idea of staying clean and warm in your home while someone takes care of the repair, stop reading now and find the phone. But, if you would rather try this yourself, you will benefit from the process and learn more about your system, possibly helping you to improve your septic system and avoid future freeze ups.

So if you’re excited about doing this yourself, find some really old clothes and read on …


How to Thaw a Frozen Septic Line – Preparation

Preparation and Materials

Project Overview

  • Level:Basic
  • Time: Hours
  • Cost: $50

Project Big Picture

  1. Locate septic holding tank.
  2. Open septic tank cover.
  3. Pass hose into septic line.
  4. Run warm water to thaw line.
Materials – Water Heater and Plumbing
Item What I used Cost
Garden Hose $20
Hose Nozzle $15
Anti Back Flow Valve $8/td>
  • Pry bar – lift cover
  • Shovel – clear snow, dig out cover
  • Old gloves – no explanation needed

How to Thaw a Frozen Septic Line – Step by Step

  1. Locate the first access cover of the septic system holding tank.

    Many systems have two access covers (one for the primary or “solid” compartment and the one for the secondary or “liquid” compartment). We are looking for the cover where the septic line from the house enters the holding tank (typically the cover closest to the house).

    Frozen septic system tank cover after digging out with cover lifted.

  2. Open access cover.

    This often requires a pry bar or crow bar to lift the concrete lid from the frozen ground. If the ground is frozen, take some time to trench out the dirt next to the lid.

    Sepic tank cover removed on frozen septic system.

  3. Gather your garden hose and nozzle.

    The nozzle should be longer than the diameter of the pipe (the pipe is typically 4″) to prevent the nozzle from turning in the pipe and therefore keep the stream pointing toward the blockage (Thanks to Nancy for the great tip).

    Non-kink garden hose to thaw frozen septic system.

  4. Find a water source.

    Ideally, you would use a source isolated from your domestic water supply, and therefore be sure the nothing from the septic systems mixes with your domestic water supply.

    Unfortunately, this may not be a realistic option. If you do use a source of water from your home — a hose faucet or utility faucet — use a back flow prevention valve to keep any water back flow from entering your domestic water supply.

    Most professionals use one of three water sources to clear ice from a frozen septic line: steam, pressurized hot water or high pressure cold water.

    I used a hose fitting connected to my hot water line from my utility room. It has the benefit of being fairly close to the septic tank and offered heated water.  Hot water is not necessary, but will speed up the process of clearing the ice blockage.

    Water source for thawing of the septic line -- use back flow prevention valve.

  5. Next, locate the septic pipe coming from the house.

    Many will have a “T” baffle and enter the tank on the side closest to the house (supply). Here is what mine looks like:

    Flushing frozen septic line - garden hose passed into septic line with water source turned on.

    Once you locate the line, you need to pass the hose, nozzle first, into the septic line so it is facing the blockage (heading back to the house).

    You may have to bend the hose slightly to get the nozzle into the septic pipe (I used a 6″ nozzle and needed to bend the hose a bit to get it in past the baffle).

  6. Turn on your water source and advance hose.

    Feed the hose into the pipe until you encounter resistance (this should be the ice blockage). Now the nozzle will be spraying water directly at the ice.

    As the ice melts, you will be able to continue advancing the hose until the ice has melted and you are through the blockage. Depending on the volume of waste water in the septic line behind the blockage, it should be fairly obvious when the ice has cleared.

    In my case a the volume of water returning into the septic tank increased dramatically and the water was soapy with white suds.

    If you are but not sure if the line has cleared, you can remove the hose (leave the water on until you are out of the septic line to prevent backflow) and have someone in the house run some water (with soap if it will help you identify the water) while you monitor for the waste water to flow into the septic tank.

  7. Remove the hose before turning off the water supply.

    Removing the hose prior to turning off the water supply will prevent back flow into the hose. Replace the septic cover and clean your tools and hose.

    To clean the outside of the garden hose, I pulled the entire length of hose through a handful of Chlorox disinfecting wipes several times and finished by pulling it through damp paper towels.

  8. Fix the underlying problems causing line freeze.

    After you have successfully thawed the frozen line, you should try to identify the underlying cause of your system freeze and make appropriate repairs. There are many excellent resources available online and I have listed a few below

Preventing A Frozen Septic Line

  • Ensure adequate natural insulation over pipe run.
    • Do not remove or compress snow over septic area (do not drive over or plow over septic system), snow has an r-value of 1 or more per inch of snow (12″ of snow = R12+).
    • Add layer of straw (R1.5 per inch) or wood mulch (R1 per inch) over pipe run and other areas of septic system or plant grass, vegetation in bare dirt areas over septic system
    • Avoid compressing dirt over septic line (cars, atvs, etc) as compressed ground freezes deeper.
  • Add insulation over and around septic system / line.
    • Add 2 – 4″ of rigid foam insulation around septic lines, and over holding tank with over lapping edges.
  • Fix or Avoid continuous, low-flow water sources emptying into septic line.
    • Fix leaking faucets, fixtures
    • Avoid using system to drain furnace condensation water.
  • Use the system regularly during cold months.
    • Regular use flushes the system and add heat to the system
    • Normal bacterial activity generates heat in holding tank.

Frozen Septic System Thaw Image Gallery

Additional Resources



  • Bruce December 7, 2013   Reply →

    Here is one more possible root cause of a frozen septic line… the ground has settled, and the line has a sag in it. The water that does not immediately drain can freeze in place if it sits in the line. You need to dig up the line and re-establish a continuous slope.

    • Cabin DIY December 8, 2013   Reply →

      Hi Bruce.

      Good point. In the past we would drive over this area with cars. I am certain the ground over the septic line has been compressed and likely there is some sag. I plan to insulate the pipe and will check the slope at the same time. Thanks!

  • George Ross February 16, 2014   Reply →

    Your advice saved me a hefty plumbing bill! At zero degrees F. There was n way i could dig up the septic without hiring a backhoe. The plugged line goes from the house into a crawl space. So i disconnected the line where it goes out of the crawl space. I put the hose in and gradually fed it about 10 feet or more. That did the trick. The excess water just pouring into the sand n the crawl space and disappeared. This was pure plumbing magic. Thanks. Cause i had no idea what to do!! Took me all of ten minutes once the tools were assembled and ready.

    • Cabin DIY February 16, 2014   Reply →

      Hey George,

      Awesome! Glad it worked. It sounds like you reversed the process and entered the soil line in the crawl space. The obvious down side to doing it this way is the emptying of the water / frozen pipe contents into your crawl space, but it sounds like you know what you were getting into doing it this way.

  • David February 19, 2014   Reply →

    Thank you for your writeup. I modified it a little bit. I was concerned about running hot water through a garden hose, but the hot water (red) hoses from the hardware store didn’t seem stiff enough to push into the pipe.

    I got a red hose and a 20′ length of PEX, as well as a PEX crimper, and garden hose to PEX adapters. The PEX worked very well for feeding into the pipe. Thanks again!

    • Cabin DIY February 20, 2014   Reply →


      Nice modification! You are right about the hot water and garden hose issue — the hose I used got fairly soft when running hot water through it. Glad it worked.

  • Maria April 26, 2014   Reply →

    Hi there, does anyone know why a line would break in the same area, two winters in a row? The area that was repaired was fine, it broke again the following winter down the line, just a foot ahead. Any ideas?

    • Cabin DIY April 27, 2014   Reply →

      Hi Maria,

      Sorry to hear about the septic line breakage.

      For the pipe to break, some force is being applied to the line in that region of the pipe run. It could be caused by compression from above (vehicles or other force on the ground over the area), movement (home settling relative to the line run, unequal ground freeze with shifting) or expansion within the pipe (pipe freeze).

      If the pipe is iron or clay, it could be just deterioration in this area — I assume its plastic and this is not the cause.

      If the pipe is plastic and breaking, some force is acting on the pipe. Consider the soil conditions, the support under and over the pipe and any force from above (cars, etc). If this is an area of traffic (driveway, etc), you probably will need a way to protect the pipe from the loads over the ground in that area. If the area over the pipe is undisturbed, think of reasons the pipe could be moving.

      Let us know what you find. Upload a photo or two if you have some.


  • Kirk May 13, 2014   Reply →

    Septic in Grand Rapids Minnesota area froze up. Has happened three times in last 10 years. Fairly easily fixed with conventional method (tank heater). Last fall added 18 inches of dirt plus foam plus straw. Bitterly cold winter so didn’t visit cabin much. Septic froze around the end of February Almost mid-May and line still frozen! Cover moved first of May. Super-insulating the pipe insured that once frozen it will stay frozen! May try your approach. Where is global warming when we need it?

    • Cabin DIY May 13, 2014   Reply →

      Wow, still frozen, that’s amazing. I assume your system is infrequently used during the winter and therefore you are not routinely adding heat to the pipe and septic system, making the insulation less of a factor.

      You could investigate wrapping the line with a heating tape or system designed to be safe with the pipe you are using (PVC, etc). I’m not familiar enough with these products to make a recommendation, but some of the newer tapes offer thermostatic temperature control and are low enough temperature to be used with plastic pipe. I’m not sure of there are products specifically designed for septic lines. From my reading, I would not recommend adding a heating tape to the inside of the line because of the risk of plugging within the line.

      Good luck. Let us know if you find a good solution.


  • Harvey December 29, 2014   Reply →

    Any idea for type of hose to navigate two 90 degree elbows? My line between the tank and field is froze somewhere. I have a 90 degree 2″ PVC line at the top of the tank where it connects to the pump line coming from the bottom. The line than goes down about 11 feet to another 90 degree and into and through the side of the septic tank and out to the mound about 40 yards away. So I need to snake a small hose through the top 90 to and the bottom 90 and out to wherever the blockage is.

    • Cabin DIY December 29, 2014   Reply →

      Hey Harvey,

      Sorry about your trouble. I don’t have 90 degree bends in my system and I haven’t had to navigate them before. I would try a very short nozzle to try and get around the corners.

  • Nancy January 14, 2015   Reply →

    Not a septic problem, but a sump pump line problem.

    I have lived in this house for 30 years, now, all of a sudden, last year and now this year 2015, the line going from my basement sump pump to the ditch has froze up. Why? I am in NE Ohio, last year we had record breaking cold spells, but not this year. Why is this happening?

    It is that black, rubber looking, 1 1/4 inch line that is froze up.

    Last year I had to run a line from the sump pump, out the basement window into a field for months until the spring thaw.

    Any suggestions how I can thaw out this pipe? Is it more than likely frozen near the open ditch it empties into? That part of the line is only about 10″ deep in the ground.

    What about using a product called Liqui-fire? Would it be safe to run that through my sump pump to get it into the line?

    What about laying those electric heating wires used on roofs to prevent ice damns on the ground over the last few feet of the line near the ditch?

    Please, any and all suggestions would be welcome.

    Thanks in advance,


    • Cabin DIY January 14, 2015   Reply →

      Hi Nancy!

      Sorry to hear about your problem with your sump pump discharge freezing.

      This seems to be a common problem in cold climates. Most sump pump discharge circuits are attached to corrugated black plastic drain pipe. This type of pipe traps water and can easily freeze. The only way to prevent ice build-up within your discharge circuit is to either have a system that stays above freezing (difficult — must be burried below frost line and still drain away from the home) or have a system that empties well and prevents residual water build up. To improve system emptying, use larger diameter, smooth wall pipe that is well pitched away from the home.

      Some recomment disconnecting the flexible plastic pipe in the winter and instead adding a larger, smooth walled short segment of pipe to direct the discharge away from the home only a short distance during the winter. Some will even just allow the water to drain next to the home during cold months — this may not be a good idea as the water will typically just find its way back to your basement.

      Each situation is different and the best solution for you really depends on your system, yard, etc. I would call a sump pump installer for help if your system is complicated. As an emergency measure you could direct you discharge into a laundry sink or drain until you can get the system fixed. Beware that many local codes prohibit discharging sump water into septic systems, as it tends to overload these systems.

      Here are some links which discussion about this very issue:

      Winnipeg water and waste – sump pump discharge
      Gardenweb – frozen sump pump hose

  • Rose January 26, 2015   Reply →

    Has anyone ever heard of the blanket that can be put on top of the ground, that cement workers use to keep things from freezing
    My line froze from my cabin to the septic tank, it is shallow and it will probably refreeze, even though they’ll be water running every day but because of lack of snow cover there is no insulation

    Am wondering if it is too late in the season to use that blanket, and if I do will I push the frost down in to the pipes more??

    • Cabin DIY January 28, 2015   Reply →

      Hi Rose,

      Thanks for visiting our site and thanks for the question.

      Thermal insulating blankets (a.k.a. insulated tarps, concrete insulation blankets, polythermal blankets, etc.) work by providing insulation over a surface. In the case of concrete, the concrete produces heat when curing and the blanket retain the heat over the concrete. The blankets retain available heat.

      In the case of a septic line, the thermal blankets would be beneficial in preventing freezing (just like snow cover, or other added insulators (straw, etc.). This is especially true if you are actively using the system and adding heat to your septic with your waste water from the home.

      If you system is already frozen, I doubt the blankets would help much in the short term. The blankets will only help to retain the existing heat, for this reason, using blankets only would like take several weeks to months depending on the heat in the ground.

      I have used thermal blankets prior to digging after the ground was frozen (late November in Minnesota) and they did a remarkable job of breaking the frost (which was relatively shallow in November) over the covered area in just a day or so.

      One issue with thermal blankets is their cost. Expect to spend $100 – $300 per blanket depending on the size. For this reason, many simply use a layer of straw or other natural insulator. I would search the internet for thermal blankets and compare the insulating R-value vs. other, less expensive insulators.

      If you didn’t mind the aesthetics, you could simply buy rigid foam board, like a foil covered polyisocyanurate foam board, from you local home improvement or hardware store. These products have very high R-values and are reasonably priced.

      Best of luck and thanks for the photo of your cozy home.



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