Drop-Ins take the guesswork out of RV or marine holding tank treatment. No measuring-no mess. Just add one Drop-In to treat a 40 gallon tank. The easy to use Drop-Ins contain a special enzyme that helps digest waste, and a blend of scented surfactant oils that trap unwanted odors in your tank. RV and marine approved, non-formaldehyde and safe for all septic tanks. Great for portable camping toilets.