cleaning agents used range from heavy-duty industrial solvents and detergents such as liquid freon, trichlorethylene and anhydrous trisodium phosphate, followed by rinsing in deionised water. these materials are now generally deprecated as being environmentally unsound and an unnecessary health hazard. some strong all-purpose household detergents have been found to do the job adequately. they are diluted with water before use, and used hot for maximum efficacy. ultrasonic agitation, shaking, pressure spraying and tumbling using glass or stainless steel beads or mild ceramic abrasives are effectively used to speed up the process where appropriate. thorough rinsing and drying is necessary to ensure that the equipment is not contaminated by the cleaning agent. rinsing should continue until the rinse water is clear and does not form a persistent foam when shaken. drying using heated gas – usually hot air – is common and speeds up the process. use of a low oxygen fraction drying gas can reduce flash-rusting of the interior of steel cylinders.