I've been trying to get the dent out of my Dr. D. headpipe for about a week now using the freezing water trick. I first tried it with no plugs and it did nothing. I then put a thermos cork in one end and it did nothing. I then put corks in both ends and it pushed one of the corks out and still did nothing. I then wired one of the corks in the pipe and it broke the wire and pushed the cork out and did nothing to the dent. I must admit the dent is not a large gentle dent, but more of a small deeper dent that might not push out easily. I also think the Dr. D. headpipe is fairly thick metal and resists dents well, but might be harder to push out a dent.