I have a toilet that supply line runs in the garage to an outside wall. A few years ago the line froze. I added insulation in the garage.

I live in Nashville where in the last two years temps have dropped under 0F.

Question, I added a shut off valve in the garage, about 3 feet before the outside wall, it then goes vertical up to the next floor. So I'm figuring shutting off the valve alone isn't enough for the extreme temps. The other night I shut off the main supply and let the water clear out. The next morning the air that came out of the overfill tube was like a rifle!

Should I be concerned with this air pressure going through a toilet? More so is shutting off the valve without draining the water okay?

Is that garage heated, insuation will not do muchif it is not heated and the water is not moving. Do not worry about that air, a vacated line will do that when the water is turned back on.

Thanks,It's not heated but heat does get in it, typically it will be in the 40's. The problem is when it goes to the outside wall in the extreme cold.The shut off valve which is about 3 feet from the outside wall is safe enough from freezing, so I guess by shutting this valve and leaving the water in it the pipe has enough water in it to freeze?Is there a special valve that I ca shut and drain the water?