I'll add to this old thread by saying I tried this on my old super pump housing that had some cracks that I finally found today. It worked like a charm!
And I only had a soldering iron with a finer tip. Should I need to redo this, I'll use a wider-tipped iron, since that will be better for smoothing the melted material--especially for the inside of the housing, where you can't work at an angle to use the side of the iron like a putty knife.