An Oleum tank required repairs during a summer shutdown. Oleum is a solution of various compositions of sulfur trioxide in sulfuric acid which is not corrosive to carbon steel. The tank had to be emptied and cleaned before repairs could be made. Once the concentration of sulfuric acid drops below 100% sulfuric acid, it becomes very corrosive to the carbon steel tank. The air space above the Oleum is also corrosive on a hot humid day. I had the bolted cover removed and then the oleum emptied. I then had soda ash to the tank and flooded it with water. As a result, the tank was emptied and cleaned without further damage to the existing tank.