HOLDING TANKS: - Depending on the size of the tank, I recommend using 1 x 30 gram tablet (white for 7 days usage, add more as required. The tablet is similar to the 8 gram but is more economical for such tanks. If you have a boat/yacht, etc sea seawater can be used, and with a Masurator, suggest crushing the tablet and installing pieces to prevent jamming. Mini Oxygen Tablets are not included in the 40x30g box. GREY WATER: - I recommend using the 30-gram tablet can be placed on the far corner of the shower base. This will clean out the pipelines leading to the tank, and can also be placed directly into the tank.