Berryman Chem-Dip Carburetor & Parts Dip (part #0996) is safe on for use on plastic, rubber, and most paints and metals, but it can react with some grades of aluminum and aluminum alloys. For that reason, we recommend that soak times be limited to 15-30 minutes per dip with a total soak time not to exceed 4 hours for aluminum and aluminum-based parts. However, for something made entirely of plastic and/or rubber, you can safely soak much longer. A good target would be soaking 30-60 minutes per dip and wiping/brushing away loosened deposits and vanish after each dip.