Also... to cut to the chase, I believe this is from the 'Peggy Hall Bible of All Things Plumbing', and is essentially the meat and potatoes of those threads I linked to above:
"Fresh Water
Maintenance" in my book:
"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.
Many people—and even some boat manufacturers—believe that keeping the
tanks empty reduce the problem, but an empty water tank only provides
another damp dark home for those “critters.”
"There are all kinds of products sold that claim to keep onboard water
fresh, but all that’s really necessary is an annua--or in especially
warm climates, 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 (including boats). The solution is approved and
recommended by competent health officials. It may be used in a new
system a used one that has not been used for a period of time, or one
that may have been contaminated.
"Before beginning, turn off hot water heater at the breaker; do not turn
it on again until the entire recommissioning is complete.
1. Prepare a chlorine solution using one gallon of water and 1/2 cup (4
oz) Clorox or Purex household bleach (5-7% 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. Open each faucet and drain
cock until air has been released and the entire system is filled. 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 several days by vehicle motion.
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.
"People have expressed concern about using this method to recommission
aluminum tanks. While bleach (chlorine) IS corrosive, it’s effects are
are cumulative. So the effect of an annual or semi-annual "shock
treatment" is negligible compared to the cumulative effect of holding
chlorinated city water in the tank for years. Nevertheless, it's a good
idea to mix the total amount of bleach in a few gallons of water before
putting it into either a stainless or aluminum tank."
