Abstract: The invention relates to a method of determining the cleanness of an apparatus comprising the steps of treating the interior of the apparatus with a solution comprising permanganate so as to cause the permanganate to react with contaminants, if any, being present within the apparatus, rinsing the interior of the apparatus to remove non-reacted permanganate, contacting the interior of the apparatus with a solution comprising peroxide and detecting a splitting, if any, of peroxide into oxygen and water. The invention also relates to a method of detecting a leakage in an apparatus and to a use of the method for determining the cleanness of an apparatus and for detecting a leakage in an apparatus.