Duo Tank Cleaner Concentrated is a powerful, concentrated, periodical cleaner for the waste-holding tank and grey water tank. For a long, clean, and fresh life of both tanks. Pairing Duo Tank Cleaner Concentrated with Greywater Fresh Concentrated is the best way to keep your waste-holding tank and greywater tank clean and fresh for a long time. Duo Tank Cleaner Concentrated will remove the tough deposits that build up over time, while Greywater Fresh Concentrated will help to prevent new deposits from forming.