Wow, lots of opinions on this. One item that was not mentioned that you probably thought of was the toilet. Back about 40 years ago, it was the most common "missed" item that I often repaired for custmers whether blowing or using antifreeze. Using that quantity, it is only smart to drain and use again providing it is not diluted.
Also, once below freezing, water will change from a liquid to a solid and expand and you can do just as much damage at 30 degrees as at 30 below zero. The only difference is the time it takes to change to a solid. Obviously longer than a few hours at 30 degrees and very quickly at 30 below.
