RhinoFLEX™ 1.7 oz. 10 Pieces Fresh Pine Holding Tank Treatment by Camco®. The Drop-Ins help control unwanted odors in your black water holding tank. The easy to use Drop-Ins contain a special enzyme that helps digest waste, and a blend of pine-scented surfactant oils that trap unwanted odors in your tank, making your camping experience more enjoyable. The Drop-Ins are RV and marine approved, non-formaldehyde and safe for all septic tanks-they're even great for portable camping toilets!