Step 1: Mix 1 part of AR5100 with 15 parts water. You can add 8 oz of AR5100 concentrate to a 1 gallon container and fill the rest with water to create a 15:1 solution. Use hot water (120F+) to decrease the amount of time needed to remove oxidation. You must mix AR5100 with water to activate the chemistry. Mixing AR5100 with less than 15 parts water will not make it more effective.
Step 2: Immerse item in AR5100 solution until all oxidation is removed. You may also add AR5100 to pressure washers. The solution will change color as it removes rust from the item, this does not mean the solution is spent, you can reuse the AR5100 solution many times until it is no longer effective.
IMPORTANT: AR5100 will leave behind a dark patina on some metals, this surface is not rust and is ready to prepare for painting or welding.
Verified review from Amazon.com: Just used this product to de-rust a Yamaha XV750 gas tank. In the past I have used acids, including muriatic to dissolve rust & have also used POR15's products. But this is my new favorite. Being water-based makes it much less hazardous to use & it was very effective on the tight, widespread rust that had taken over the inside of this particular tank. The tank had been closed & stored indoors for several years, so the rust was mostly the result of condensation, not exposure to the elements. The Archoil product works slowly; I moved the tank into different positions @ periods of 4-8 hours to try to soak as many nooks & crannies as possible. This was also necessary because the concentrate makes 2 gallons of treatment solution & the tank holds about 4-4.5 gallons. I left the cap, petcock & low-fuel level hardware in place during the treatment &, when the tank was drained, they were removed & were as good as new. Had to dump most of the solution out the neck of the tank, then dribble the rest out through the petcock & warning light openings. Hung the tank on the wall & used the output of a small vacuum cleaner to force air through the tank to dry it out. Amazing how dark & disgusting the solution had become. The maker says you can use it multiple times, but I think this batch is done. SO, I'm ordering some more to treat a 40-year old Yamaha tank!
PS: I did not apply any liner resins to the inside of this tank after treatment. The inside surface looks that clean. I will, however, use a fuel filter in-line to my newly-cleaned carbs.