G'day Mark,
We leave the bunks/screws in and fill. It has sat there for a few months and never tasted any different.
I've only ever drained ours once, that was to remove the 120lt S/Steel tank and have some welding done to it.
Don't believe I've ever emptied the water out of the 60lt factory tank poly tank.
I've heard some people drain them when traveling home, saying they will dry out and leave them empty till their next trip.
We also carry with us some Johnson & Johnson baby bottle sterilizing tablets, just in case we come across some dodgy water, they have a real strong Chlorine taste and smell.
Anyway, that's what we do.