The marks are on top of the lacquer (automotive standard lacquer), which is protecting the paint inside. This could be easily removed by applying any good quality rubbing polish (3M) with the help of the soft cloth and you will see the marks vanishing right in front of your eyes. We also apply inside of the tank with sealer, but we encourage our customers to apply their inside lining to give extra protection. Any rust seen inside is already covered with transparent lining applied by us. Another inside lining by the customer at their end will give enhanced protection.