Forespar ReFresh Head and Tank, Part No. 770063 16 Oz.

Not a cover-up fragrance,  absorbs and neutralizes odors. Pour 1 oz in head and flush with 1 or 2 quarts of fresh or salt water. Kills odors up to 4 months. Starts working immediately on liquids and solids.  Reapply deodorizer after tank is is discharged. 1 bottle fully treats your holding tank 16 times (20 gallon tank). Graduated container shows how much to use for your tank. Water based, non-toxic & biodegradable.