We have a vacation home in central NH which up to now we have left heated at 50 degrees over the winter when it is unoccupied. With the price of oil so high, I'd like to leave the heat off. The heating pipes have antifreeze already, however, when I drain the house I need to use antifreeze in all the sinks, toilets, tub drains, etc. I'm concerned about the toxicity of antifreeze, first, to humans, as it will be in every drain, and,second, to the environment when it drains into the septic system in the spring. How can I find out if this stuff is REALLY safe?