Check the listing for details. Forespar ReFresh Head And Tank Odor Killer. Condition: New. Listed at 26.20 USD. ReFresh Marine Head & Tank Deodorizer is an extremely effective biodegradable odor killer. It is not an enzyme, but rather uses chemical technology to absorb and destroy holding tank gases and odors for up to four (4) months. Holding tanks contain not only liquid, but also solids which may dry on the inside of the tank, hoses and fittings. ReFresh penetrates and binds to odor causing solids, and eliminates the odor-causing components.Not a cover-up fragrance, absorbs and neutralizes odorsPour 1 oz in head and flush with 1 or 2 quarts of fresh or salt waterKills odors up to 4 monthsStarts working immediately on liquids and solidsReapply deodorizer after tank is discharged1 bottle fully treats your holding tank 16 times (20 gallon tank)Graduated container shows how much to use for your tankWater based, non-toxic & biodegradable