For long-lasting freshness and hygiene for your 2 tanks. A 800 ml bottle allows you to either 4 cassette cleaners (4 x 200 ml) or 1 cassette cleaning (200 ml) + 1 grey water tank cleaning (600 ml). It can be used in conjunction with the Grey Water Fresh concentrate. 500577 Use 2-3 times a year for optimal results.For long-lasting freshness and hygiene of your 2 tanks. A 800 ml bottle allows you to either 4 cassette cleaners (4 x 200 ml) or 1 cassette cleaning (200 ml) + 1 grey water tank cleaning (600 ml). It is used in addition to the Grey Water Fresh concentrate. 500577 Use 2 to 3 times a year for optimal results.