I am also in for the winter, but the sea-cocks will be open after the LIYC dock commissioning, which is the first Saturday in April. So for me that is somewhat of a splash day. I like water flowing so I can begin the cleaning process, and also to commission the water systems.
See Below... I got it off of a RO posting a while back. I have a modified the version a little.
Fresh Water System Commissioning
Fresh water system problems--foul odor or taste--are typically caused by allowing water to stagnate in the system. 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 that 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 annual or in especially warm climates, semi-annual re-commissioning 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. 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 re-commissioning 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 re-commissioning and the first bucketful afterward--should be discarded.
1. Using 1 cup (8 oz) Clorox or Purex household bleach (5% sodium Hypochlorite solution) for each 10 gallons of Tank capacity, with the tank empty, pour chlorine solution into tank. If you have a 40 gallon tank, use 4 cups.
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 8 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, you may want to repeat this a few times.
If you feel needed ( I have not done this)
5. To remove excess chlorine taste or odor which might remain, prepare a solution of 1-3 quarts white vinegar to an average size tank and allow this solution sit a couple of hour with a pressurized system.
6. Drain tank again through every faucet, and flush the lines again by fill the tank 1/4-1/2 full and again flushing.