I have a York Guardian furance for my cabin. I shut the cabin up in the winter when I am not there. The cabin can get to below zero inside. How do you put anti-freeze in the internal condensate trap to keep it from freezing.

Is it an internal trap? Mine is on the outside and drains into a condensate pump. Some use a running trap with a T and a vent. I would pour some antifreeze in there. Can't need more than a couple of teaspoons.