I have used the Evapo-rust on a tank and it was the easiest way I have ever tried to remove rust from a tank. I poured it in and left it for a few hours and then moved the tank to expose different areas to the fluid. I kept moving it every so often (depended mostly of if I was sleeping or working).
I only had access to a few litres of it as it goes for almost 10 bucks a litre here after tax thus the constant moving of the tank.
It does leave a fine black coating after it has done it's reaction. I had tried it on a few rusty tools etc and it simply wiped off with a rag, so I just rinsed out the tank a few more times and it came squeaky clean.
You can also replenish it with water when your amount is too low, but it will slow it down somewhat so do not like ....buy 1 litre and then add 5 gallons water as you will be disappointed for sure.
