The experiment Go further down into the body of this post to see photos of the experiment.
Water freezes at the same temperature even if you live on Mars and only expands by 8% so a little moisture in the lines will not do a thing. I previously posted
We have blown the lines and filters out, the valve in the commode blows air, all the valves are cracked, made sure the water pump sucks air, all the tanks and HW heater are drained. We have only put pink stuff is in the drain traps and commode bowl during the winter months and have NEVER had a problem.