When did you last see your water tank?

We've had Starcross for five years now and the people we bought from had her for at least two so we know for a fact that in all that time no one has ever checked the tank on board that contains the domestic water supply. This started to bother me after I read an article in one of the waterway magazines about water tank hygiene and the need to check and clean them regularly. Hilary's training as a microbiologist confirmed this but we'd never actually got around to doing it. We've generally only used the water for washing anyway and keep a separate supply for drinking and cooking in plastic bottles topped up regularly whenever we pass a water point, but even so it was beginning to bother us.
So, last week with a few days to spare at Norbury Junction I finally had a look. I knew where the tank was: the presence of the filler tube in a bow locker was a bit of a give-away as was a metal plate bolted to the floor of the well deck, which was obviously the means of access. Now this plate had not been disturbed for at least seven years, during which time it had been painted over at least once - it was not going to be easy to move. All thirty-four bolts holding it in place were seized solid and all required a spanner, a mallet and a large helping of brute force and ignorance to remove. The plate still refused to budge. Next step was to scrape the paint from the edges of the plate then insert two screwdrivers, driven home by the mallet, to act as wedges after which it could be lifted clear.
I'm not sure what I expected to find. I had read that the tank could either be steel - in which case I thought I might find a rectangular tank with a lid or separate inspection hatch - or plastic, when I'd see a plastic or polythene bag - possibly collapsible for removal. What I certainly didn't expect was what I saw - water! Directly underneath the plate. It was clear enough, which was a relief - but also clear enough to be able to see the several layers of rust on the bottom! There was nothing for it but to swiftly replace the lid - and all 34 bolts!
So, that's another job that needs doing and a long one it will be with emptying, drying out, scraping, painting and refilling several times -all  assuming  its in a condition to save. We will work on the basis that as we've survived this long we can go on a bit longer - but we certainly won't be drinking the water - and get round to it when it won't actually get in the way of boating.
So, how often does everyone else check theirs?