We annually recommission our water tank in the spring. I put 60 ounces of chlorine in 75 gallons, run all taps until all smell heavily of chlorine. Leave the solution sitting in your tanks for a minimum of 4 hours, preferably 6. Empty all the heavily chlorinated water through all of your outlets. Once empty, I insert fresh water hose into fill port and match the volume in to that out that it takes for all my outlets to be open. I flush the system like this for about 30 minutes, and then taste the water to see how much chlorine is still there, if too much, the repeat flushing until can barely taste chlorine. then fill the tank. Do not tun on the HWH. After the tank is full, I flush all out again, then drill. By now most of the chlorine is gone, but I usually let sit overnight and then reflush all of the tank again. That is going to completely sanitize your system. Last spring, after doing this, I put in a Safeh20 system with two filters and a. UV light. The SafeH20 unit sits after the tank and before the manifold that distributes the water to the outlets and HWH. We use the water for everything we do and have not ever had a problem using this technique. We got water from a number of sources during our cruise to Florida this past winter and had no problems and felt very safe drinking, cooking, washing dishes, showering and brushing our teeth with the onboard water. We carried some bottled water on our offshore portions just in case we developed a leak and lost our water. the Safeh20 system is good for 3 gallons a minute flow rate and our onboard water pump is rated as 2.8 gallons per minute. Look them up on their website and you will find that the unit kills nearly anything that can get in water that is harmful. I will change out all the filters and the uv light late spring. Cot so the replaceable components is about $45 per year. Small price to pay for ultra clean water.
