We have recently purchased a second hand sailing yacht and would like to know what is the most effective way of cleaning out/ sterilizing the drinking water tanks and associated plumbing.
In the same process with the current boat and her flexible tanks.
If there is solid contamination (black mould) on the pipes and tanks, there's no real alternative to taking them out, or flushing through with a biocide and hot water to dislodge the crud. Brushing or wrapping a hunk of cloth onto a piece of line and pulling it through may help. You can go on doing this for a long long time
We had to junk one flexible tank, and replace a transparent plastic pipe. Any new pipework or tanks get treated with Milton tablets (as recommended by the Forum chemist VicS).
Choice of biocide is a bit difficult, as getting rid of the flushings should really be treated as Contaminated Waste.
Prevention of foreign bodies in incoming fresh water is essential. You can fit a fine wound polypropylene filter (from e.g. Jewsons, or Plumb Centre) to prevent the ingress of 'bits' when you fill up, but biologically active material must also be excluded.
We had an O ring failure in the filler cap, allowing sea and rainwater, and general marina dust and bird carp to enter the system over a long period. This was Good News for the bugs in the tanks, but not for us.
Ideally, I'd like a General Ecology filter system for cold drinking water out of one tap, and another unfiltered tap from the same source for cooking/ washing up.
There was a thread on just this subject late last year, and 'The Headmistress' provided an excellent detailed post on how to do this and keep it sweet therafter. I followed her instructions this spring and the resulting crud that came out was quite startling. I quote the main points as follows:
" 1. Prepare a chlorine solution using one gallon of water and 1/2 cup (4 oz) Clorox or Purex household bleach (5% sodium Hypochlorite 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 3 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).
5. Fill the tank again with fresh water only, drain again through every faucet on the boat.
6. To remove excess chlorine taste/ odour which might remain, prepare a solution of one quart white vinegar to five gallons water (20:1) and allow this solution to agitate in tank for several days by vehicle motion.
7. Drain tank again through every faucet, and flush the lines again by filling the tank ¼ to 1/2 full, to again flushing with potable water."
This will now be an annual task for us from now on.
I have a very good friend, he calls himself Dr Sludge (Polite version) He does have a doctorate in all things about water, how to treat it, use it, dispose of it.
I can confirm as posted above and frequently on other threads on this subject.
Sodium Hypochlorite is the way to go, as per Rudolfs post above for that deep clean.
Cheap bleach is best.(Vics)
Then a couple of milton tabs each time you refill during the season.