Either way will work. I used the pink stuff in the cabin toilet when I put it away for the winter. One time I came back when it was -40f and it was frozen solid. I took my jackknife to it as a test and it came apart like a snow cone. Toilet was just fine in the spring.
Like a prior post stated it doesn't expand like water does when it freezes. Quote:
"Water is one of the few exceptions to this behavior. When liquid water is cooled, it contracts like one would expect until a temperature of approximately 4 degrees Celsius is reached. After that, it expands slightly until it reaches the freezing point, and then when it freezes it expands by approximately 9%."