Get a piece of 4", schedule 20 sewer pipe and a cap to fit it, that is long enough to hold the bars of clamps. Glue cap on one end. Support sewer pipe vertical, and fill with white vinegar. Slide heads of clamps all the way closed, then let bars hang down into vinegar, and soak for 30 minutes. Remove, scrub off glue, rinse with water to remove any remaining vinegar, or glue. After soaking, you could use power washer to make job easier. Dry bars very well, using either heat gun or blow dryer. Vinegar can be saved and reused next time.