I would like to report on how I did last summer on welding a crack in my diesel aluminum fuel tank on my tuna boat. I am alive and well. Welding from the inside was the only way. There was a 24" hole for cleaning so I did not need to cut a hole. First I cleaned with a water based cleaner. Next I wire brushed the entire tank. Tank seemed good and clean to me. Next I bought a RAE Systems UltraRAE 3000 VOC tester. This was for testing to see if I needed to clean further. On the first test I had 15PPM. This is very clean. My CNC machine shop at the end of the day reads 30PPM. So I was good to go. It was tight working inside but had no choice. I did use a Hooka for breathing air AND IT WORKED GREAT. My helper would turn a large blower on as soon as I stopped welding , than off as I started again. All seams have three full beads over the old. It took about six hours of weld time but I am happy with how it turned out. The VOC tester did cost $5500. but took the guess work out.