Camco's Rhino RV holding tank cleaner Drop-In's contain a powerful enzyme complex that helps clean your RV's black water holding tank. Just one Drop-In treats up to a 40 gal tank. These easy-to-use Drop-In's are pre-measured and safe for all septic tanks. This product does not contain pesticides, biocides or the toxic formaldehyde-releasing ingredient (No Suggestions). Made proudly in the USA.