About every three months when I change our fresh water filter I fill the filter housing about 1/2 full of bleach and then fill our 100 gallon water tank with water. We then disconnect from the city water supply and use the water from the tank. This puts bleach water through all our pipes and down all our drains. The amount of bleach does not seem to hurt our pipes or ourselves. Everything smells great and no mold. A word of caution: You may have to adjust the amount of bleach according to your water tank size.