I do not remember the formula

I inspected this tank inside and out. The only rust I can find is surface rust and it cleaned off easily with a wire brush. I am going to chemically treat the inside for rust and then reexamine it. All the welds are in perfect shape with no defects at all.
Once I finish treating the inside with the rust chemicals, I will put my camera down it again and reinspect all the welds from the inside.
I am truly amazed the condition of this tank, onced I cleaned the outside. Even the plugs came off without a problem once I gave them a quick squirt of WD40