BTW, the bleach, if used as directed, will hot harm anything, either your tanks or pluming, IF USED AS DIRECTED! It would not be good to leave it in the tanks or lines for an extended period,as there is a possibility of damage to systems exposed to full strength bleach for an extended period of time. Following a good cleaning, the clorination in city water should be sufficient. Please note however, that the chemicals and minerals in city water can and will create pwoblems in any system after a period of time. Witness the mineral buildup on your faucets and fixtures in your home.