I was attempting to weld some 16g tube today and I always hit it with a flap disk and wipe clean with acetone on the outside, but I noticed that I was having one hell of a time because of the contaminants on the inside of the tube where getting pulled up to the surface.

I didn't really have much probs with not cleaning the inside of the tube when welding
.120 tube, but the thinner stuff was popping and spewing.

What is your prefered method to cleaning the inside of a tube before welding? or do you even bother?