Antifreeze in Septic Tank

By Stephen methew

As winter approaches, homeowners with septic systems might be considering the use of antifreeze to prevent freezing. While antifreeze can lower the freezing point of the wastewater in your septic tank, it’s important to understand that pouring antifreeze directly into your septic system is not recommended due to potential environmental and system risks. Here’s everything you need to know about using antifreeze in your septic tank.

Antifreeze in Septic Tank

How Antifreeze Affects Septic Tanks

Common antifreeze, such as automotive or RV antifreeze, contains ethylene glycol, which is a toxic chemical. If this chemical were to leach from your septic tank into the drainage field, it could contaminate the groundwater, posing a significant environmental hazard. Due to this potential for contamination, septic system experts generally discourage the use of antifreeze containing ethylene glycol.

An alternative type of antifreeze is propylene glycol, found in many RV and marine antifreeze products. While it biodegrades more readily than ethylene glycol and is less likely to damage your septic system, it’s important to use it cautiously to avoid harming the beneficial bacteria in your tank.

Addressing Freezing Concerns

During freezing temperatures, there’s a concern that the wastewater inside your septic tank and the pipes leading to the drain field might freeze, leading to damage. However, septic tanks rarely freeze completely due to the warmer waste that enters the tank from your home.

Baffles and insulation also play a role in preventing freezing by slowing down the transfer of heat. Generally, freezing is a greater concern in the pipes and distribution box rather than inside the septic tank itself, unless you live in an area with sustained subzero temperatures.

Effective Practices to Prevent Freezing

Instead of using antifreeze, follow these effective practices to protect your septic system from freezing:

Insulate Aboveground Pipes and Tanks

Wrap pipes and inlet/outlet pipes on tanks with insulating foam. Secure a fiberglass lid insulation kit onto the access openings.

Let Tanks Sit Low

Avoid having tanks pumped out late in the fall. The extra waste in the tank acts as insulation.

Use a Smaller Riser

Opt for a 6 to 8-inch riser instead of a 24-inch size to prevent surface frost penetration.

Add More Soil

If your septic tank lacks sufficient soil cover, adding extra soil can provide insulation.

Divert Runoff

Prevent rain or meltwater from pooling on your drain field and freezing.

Plant Deep-Rooted Plants

The roots of these plants help extract moisture and insulate the soil above your drain field.

Heat Tape for Pipes

Use UL-approved heat tape to maintain temperatures above freezing.

Temporary Heat Sources

In extreme cold temperatures, you can place portable heaters or heat lamps near exposed pipes and tanks to prevent freezing.

Professional Assistance

Consider hiring an experienced septic contractor to perform the necessary winterization steps.

Safe Alternatives to Antifreeze

If you’re concerned about freezing and still want to take precautionary measures, consider these safe alternatives to traditional antifreeze:

  • Propylene Glycol-Based RV/Marine Antifreeze
  • Food-Grade Glycerin
  • Calcium Chloride Flakes
  • Denatured Alcohol (Ethanol)

When using these products, only introduce small amounts through your internal plumbing. Never pour them directly into your septic tank. Keep in mind that the likelihood of your septic tank itself freezing is relatively low. Focus your efforts on protecting exposed pipes and drainage areas.

FAQs About Antifreeze in Septic Tank

Is it safe to use RV antifreeze in my septic system?

Yes, but use only antifreeze made for RVs that contains propylene glycol, not ethylene glycol. This safer alternative is specifically designed for draining into sinks and drains. Follow the recommended dosage and use sparingly.

How should I add antifreeze to my septic tank?

Never add antifreeze directly into your septic tank. It should only be introduced through sinks and drains so that it enters the tank gradually along with regular household wastewater.

Can I use windshield washer fluid in my septic system?

No, windshield washer fluid contains methanol, which can harm the bacteria responsible for breaking down waste in your septic tank. Avoid pouring it down any drains that lead to your septic system.

Is it a problem if my septic tank freezes?

Partial freezing in the inlet and outlet pipes won’t cause immediate damage to your system, but it could lead to backups and clogs. If the tank itself freezes completely and expands, it could rupture the tank walls. Preventing any freezing is the best approach.

How often should I add RV antifreeze during the winter?

Follow the instructions on the product packaging, which usually recommend adding 1 to 2 gallons per month during freezing months. Using too much antifreeze can harm your system. Stop adding it once temperatures are warm enough to prevent freezing.

At what temperature will my septic tank freeze?

Septic tanks are less likely to freeze than external pipes due to the waste inputs. Undiluted sewage in a tank may freeze at around 20°F. With the presence of bacteria and effluent, tanks are unlikely to freeze until temperatures drop to roughly -10°F or lower.


While the idea of adding RV antifreeze to your septic tank might seem like a convenient solution for winterization, it’s advisable to avoid pouring any type of antifreeze directly into your tank. Instead, focus on insulation, heat sources, and other methods to prevent freezing. Concentrate your protection efforts on exposed pipes and drainage areas, rather than the tank itself. By taking proper precautions, you can safeguard your septic system from freeze damage without introducing potentially hazardous chemicals into the environment.

  1. United States Environmental Protection Agency (EPA). (n.d.). Septic Systems: What You Need to Know.
  2. Penn State Extension. (2021). Septic Systems: Operation and Maintenance of Onlot Systems.
  3. University of Minnesota Extension. (2019). Septic Systems.
  4. University of Missouri Extension. (2021). Wastewater Treatment.
  5. National Environmental Services Center. (2021). Aerobic Treatment Units: A Safe and Effective Wastewater Treatment Alternative.
  6. State of California Water Resources Control Board. (2012). Graywater Standards and Definitions.
  7. Ohio Environmental Protection Agency. (2015). Residential Sewage Treatment Systems.
  8. Washington State Department of Health. (2021). On-Site Sewage Systems.

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