No need to open tanks to recommission
Although most people think only in terms of the tank, the plumbing is actually the source of most foul water, because the molds, mildew, fungi and bacteria which cause it thrive in damp dark places, not under water. There are all kinds of products sold that claim to keep onboard water fresh, but all that’s really necessary is an annual or, in especially warm climates, a semi-annual recommissioning of the entire system—tank and plumbing. The following recommendations conform to section 10.8 in the A-1 192 code covering electrical, plumbing, and heating of recreational vehicles. The solution is approved and recommended by competent health officials. Before beginning, turn off hot water heater at the breaker; do not turn it on again until the entire recommissioning is complete. Icemakers should be left running to allow cleaning out of the water feed line; however the first two buckets of ice—the bucket generated during recommissioning and the first bucketful afterward--should be discarded. 1. Prepare a chlorine solution using one gallon of water and 1/2 cup Clorox or Purex household bleach (5% sodium Hypochlorine solution ). With tank empty, pour chlorine solution into tank. Use one gallon of solution for each 5 gallons of tank capacity. 2. Complete filling of tank with fresh water. Turn on every faucet--hot and cold--on the boat let water run until what's coming out smells strongly of bleach. Turn off the water, but do not turn off the pump; it must remain on to keep the system pressurized and the solution in the lines. 3. Allow to stand for at least three hours, but no longer than 24 hours. 4 Drain through every faucet on the boat (and if you haven't done this in a while, it's a good idea to remove any diffusion screens from the faucets, because what's likely to come out will clog them). Fill the tank again with fresh water only, drain again through every faucet on the boat. 5. To remove excess chlorine taste or odor which might remain, prepare a solution of one quart white vinegar to five gallons water and allow this solution to agitate in tank for a couple of days. 6. Drain tank again through every faucet, and flush the lines again by fill the tank 1/4-1/2 full and again flushing with potable water. This not only cleans out the entire system, but also gets rid of all anti-freeze taste and odor.
