I did 2 tanks with in the last month. There are a lot of videos out there on you tube about cleaning tanks. If you watch 10 videos you will see 10 different ways to do it. The first tank I did wasnt really that bad but it had a little bit of rust so I did it. I tried using Muratic acid first, but would not recommend it. It will peel off your clear coat if not careful. I then used the POR 15 kit (3 items ). Seemed to come out pretty good, its hard to tell when you cant see the whole inside of the tank. The second tank I did was really bad. I filled the tank up with vinegar and let it sit for a week. The rust that came out of the tank was incredible! Next I used the POR system again and continued to get a lot of rust out of the tank. After I was satisfied I got as much rust out as I could I coated the tank. Seemed to turn out good but only time will tell. The way I look at it is if you have rust in your tank, try to catch it early. Cleaning and coating a tank is very time consuming with no guarantees.