4 Steps to Winterize Portable Sanitation Equipment Before the First Freeze

As subzero temperatures approach, PROs face one of their most critical winter challenges: preventing ice buildup and tank freeze-ups. Freeze prevention is essential to protect your investments, avoid holding tank cracks, and stop service disruptions. None of your service techs want to roll up to a frozen tank!

1. Perfect chemical ratios

Your first line of defense when winter hits is maintaining proper chemical dilution in holding tanks. Additives like antifreeze and magnesium chloride can prevent holding tanks from freezing over, but only if you get the mixture ratio right.

First, establish your baseline ratios. Amounts of additives are based on anticipated ambient temperatures, the type of additive, and your expected unit usage. As waste increases in the tank, dilution occurs, raising the slurry’s freezing point.

For many PROs, propylene glycol is the commonsense response to cold temperatures. For standard holding tanks, maintain a target concentration of 25% to 30% propylene glycol mixture for mild frosts (down to 20°F/-6°C), and scale up to 40%-50% target concentration when facing sustained subzero temperatures.

For best results, use the following equation to determine the amount of antifreeze to add to your tank:

• Antifreeze Volume (gal) = Total Tank Capacity (gal) x Target % Concentration
  • Ex. 1: 60-gallon holding tank experiencing subzero temperatures.
    • X = 60 x 0.50 = 60 x 50%
    • X = 30 gallons of antifreeze
  • Ex. 2: 120-gallon combined holding tank experiencing mild frost
    • X = 60 x 0.3 = 120 x 30%
    • X = 40 gallons of antifreeze

Salt-based brine solutions are another popular solution for freezing nonpotable water/wastewater tanks.  When using salt/magnesium chloride brine mixtures for nonpotable waste tanks, ensure complete solubilization before filling to prevent salt crystallization at the bottom of the tank, which can damage vacuum pumps during service.

Before adding a brine solution, determine your “target mixing ratio,” or the amount of magnesium chloride needed per gallon of water, depending on temperature. The magnesium chloride mixing ratios are more nuanced than that of antifreeze:

• 26°F/-3°C: Use 0.50 lb per gallon
• 19°F/-7°C: Use 1.00 lb per gallon
• 11°F/-12°C: Use 1.50 lb per gallon
• 0°F/-18°C: Use 2.00 lb per gallon
• -20°F/-29°C: Use 2.25 lb per gallon.

Note: 2.25 pounds of magnesium chloride per gallon of water is the “eutectic maximum.” Adding any more magnesium chloride than that will cause the slurry to freeze faster, as the salts won’t dissolve, and may precipitate and settle to the bottom of the tank.

Once you determine your target mixing ratio, use the following formula to determine the total weight of magnesium chloride to add to the tank:

• Total weight of magnesium chloride (lb) = Tank volume (gal) x Target Mixing Ratio (lb/gallon)
• Example: A bank of restrooms that are serviced weekly shares a 75-gallon holding tank that needs to be winterized. Current temps are hovering around 28 degrees F but are expected to drop to 10 degrees F over the next week.
  • Target mixing ratio: 2 lb per gallon
  • Tank volume: 75 gallons
  • 75 gallons x 2 lb = 150 lb total magnesium chloride

2. Select eco-safe deicers

The right deicer should keep you compliant with environmental regulations and employees safe. Make sure any antifreeze you use is nontoxic, biodegradable propylene glycol. The other common antifreeze — ethylene glycol — is toxic to humans, wildlife, and water and wastewater treatment processes.

Similarly, when choosing a commercial brine or deicer, look for biodegradable formulas. Commercial deicers are especially helpful for removing ice from step pads and porta potty thresholds without corroding aluminum or plastic parts. Using deicers is good customer service that also proactively protects your employees.

3. Establish winter-specific protocols

To prevent costly tank cracking and mechanical failures, you need a systematic prefreeze treatment plan and integrate it into your pretrip checklist. Start by charging tanks with winter-formulated deodorizers and antifreeze solution before units leave the yard. Ensure the solution covers the bottom of the tank completely so initial waste doesn’t freeze directly to the tank floor. Tailor your pre- and post-trip checklists to the seasons so service techs aren’t scratching their heads when you ask about season-specific protocols.

Before deploying a portable restroom in winter, apply silicone-based lubricant to slide valves, rubber gaskets and dump valves. This prevents ice bonding and rubber seals from degrading in cold temperatures. Maintaining proper antifreeze/brine ratios in holding tanks will also protect slide valves. Otherwise, slide valves will come under immense pressure when ice freezes and expands.

Protocols for deployed units are also important and should include guidelines for extreme freeze advisories, overnight tank-draining procedures and when to temporarily stage equipment indoors to avoid severe exposure.

4. Don’t neglect the fine details

While propylene glycol- and salt-based deicers are biodegradable, there are precautions you can take to protect yourself, your team and your equipment. First, emphasize the order of operations: Salt-based brines must be added to water, not the other way around. Adding a salt brine first causes clumping in the tank and lessens its effectiveness. Second, stress the importance of immediately cleaning splashes with freshwater. While not as corrosive as other biological agents, at best, standing puddles of deicer can leave an unsightly, chalky white residue or, at worst, degrade equipment.

Also, if you use a premade 30% liquid magnesium chloride solution, it meets the targeted mixing ratio as is and can be poured directly into the tank or blended with a base liquid. Check the manufacturer’s instructions for specifics.

Use this sample PRO Checklist to create your own winterization protocol.