Water Tank - Winter Layup

[petem]

We'll be back on the boat in a couple of weeks for the final trip of the year. In previous years I've simply filled the water tank and then drained it and refilled it in the Spring. However, I suspect that there's a better way of keeping the tank clean and germ free.
I've aware of Puriclean but this seems to be a Spring / cleaning treatment than something to leave in the tank over the winter. Does anyone have a regime that they can recommend to prevent the water from going stagnant over the winter and then cleaning the tank in the Spring? We're in the Med so don't need to drain the tank to prevent freezing.

 

[jrudge]

I don’t do anything but a cup of bleach ( chlorine ) will keep it bug free

 

[rafiki_]

I have used a small amount of Milton (nappy cleaner) in the past, but this does leave a tang to the water despite flushing. Frankly i have used nothing for the past few years, and the water has been fine. Note we don’t use the water for drinking, but it has no smell to it.

 

[Momac]

I leave the tank empty over winter ( primarily for frost protection).
A full tank flushed through the taps in the spring seems sufficient .
We prefer not to drink tank water.