It is essential that a toilet fluid should kill harmful bacteria and germs to prevent them from multiplying. Elsan Blue's powerful anti-bacterial formula kills them on contact whilst eliminating unpleasant odours. Elsan Blue and Double Blue are the only fluids you can buy that exceed British Standards. That’s why Elsan toilet fluids are chosen by caravanners, boating and camping enthusiasts alike. Dosage: Add 30ml of Elsan Double Blue to the waste holding tank for every 10 Litres of waste tank capacity. Then add 2-3 Litres of water. British Standard Number: 2893:1989.