Portable toilets, whether the stand-up style found at work sites or the smaller versions used for RVs and hunting camps, are at risk of freezing when exposed to temperatures below 32 degrees Fahrenheit. If you employ preventive techniques recommended by the toilet makers, you will prevent the toilet from freezing up on you in your time of need. Use the techniques before the weather turns cold as once a toilet freezes up, you will not be able to get the chemicals into the toilet.
Pour one cup of the antifreeze into the toilet bowl. Use one cup for every 5 to 6 gallons of water the toilet bowl holds.
Flush the toilet so the antifreeze goes into the holding tank and through the pipes.
Pour a half-cup of rock salt into the toilet and flush the crystals down into the tank.
Consult a mixture chart if your portable toilet is larger than a small, camp-style portable toilet (see Resources).