boat holding tanks full or empty over winter

[CHKIWI]

Hi we putting our yacht up on the hard for winter
What should I do about the boat holding tanks full of fresh water or empty over winter?

Cheers
Colin

 

[rivonia]

Holding tanks should be empty if there is the slightest chance of any frost. As an aside we always have our holding tank empty at all times and after a period of time just flush it through, with fresh water.

 

[CHKIWI]

Hi we are in south Turkey so no ice or frost
Cheers
Colin

 

[Mistroma]

I've always left our tank empty over winter even with zero chance of frost. Leaving it full of fresh might help soften deposits but then I'd have problems emptying before launch if any work needed to valves etc. I don't see it as an advantage and prefer to leave it empty and as clean as possible.

I always start trying to clean the system a few weeks before lift out:
1) Empty en-route and fill with fresh water which lies there for a day.
2) Pump some hydrochloric acid through the system 4-5 hours before leaving marina
3) Empty and flush at sea
4) Repeat 1-3 once more

I'll try a final fresh water flush by pumping 20-30 litres from shower prior to entering marina for lift out. I've still seen some debris When I've done this in still water well offshore. However, our tank always looks clean at start of the seasons (checked with strong light shining through side) and never had any smells from that system.

I was thinking of using some caustic soda in fresh water instead of the final acid rinse. It might dislodge some of the small bits left on side of tank close to the bottom. It shouldn't do any harm but might just shift a tiny bit more.

 

[macd]

I was thinking of using some caustic soda in fresh water instead of the final acid rinse. It might dislodge some of the small bits left on side of tank close to the bottom. It shouldn't do any harm but might just shift a tiny bit more.

I doubt caustic soda would have any benefit, but it may harm the rubber bits in your pump (unless you don't fill it via the pump). A few weeks ago there was a long thread about the effects of assorted chemicals on neoprene parts: might be worth finding.

 

[mocruising]

We flush well then close then put a solution for holding tanks into the tank and top off with fresh water, to about half full. Area where there is no heavy frost. It seems to work and stops the smell some complain of.

 

[vyv_cox]

This year I decided to open the inspection hatch on our holding tank to inspect, first time after five years installed. It's a Tek-tanks custom one, 50 litres. Flushed through a few times first using fresh water via the toilet. On opening up there was very little smell but quite a lot of scale. This was relatively easy to remove by banging the sides of the tank and later on with a scraper and water flush. As I have found previously with toilet internals, the scale was hard and would have taken a lot of hydrochloric acid to clear, so far more effective to use the mechanical methods. Within about 15 minutes the inside was scale clear and spotlessly clean.

 

[CHKIWI]

Thanks for the in put, its a bit hard to just clean out the tanks here in Turkey
As we are in a marina, they all would like to know what you are up to.
Have put two loads of fresh in I think next year will give them big clean out by hand out of the marina
Cheers
Colin

 

[Mistroma]

I doubt caustic soda would have any benefit, but it may harm the rubber bits in your pump (unless you don't fill it via the pump). A few weeks ago there was a long thread about the effects of assorted chemicals on neoprene parts: might be worth finding.

Yes, it's going in via the deck opening and might remove a few bits of organic debris. Not trying to remover calcium deposits (there usually aren't any). I know that it isn't good for chromium plating but doubt there's much left on the current valve which is due for replacement. Can't see it being a major problem at the time, temp. and concentration I'll be using.

Thanks for the warning though, it's been around 30 years since I worked as a research & development chemist and that was in organic chemistry so lots of time to forget anything I knew about inorganic (not a lot).