Water tanks require sanitizing on a yearly basis or after they have been connected to a city water source for an extended length of time. To sanitize the freshwater system, add bleach at the rate of one-quarter cup of bleach for each gallon of water in the tank. The tank is then rinsed and refilled. This procedure disinfects the hot water and freshwater tanks.
Black water tanks hold human waste. Chemicals containing enzymes are added to the tank, through the toilet, to keep odors to a minimum. The chemicals help to break down solid waste and paper products. In hot weather, the black water tank may require more chemical treatment than usual to keep odors at bay.
The gray water tank does not usually require the addition of chemicals to keep it clean and bacteria-free. Gray water tanks collect water from sinks and showers. Bacterial buildup is not normally a problem, as soap products tend to inhibit bacterial growth. Chemicals are available to help break down the soap residue, but these products are not necessary for the operation of the gray water system.
