Want a quick, easy and safe solution?
Keep tanks filled...less bacteria to grow in a full tank....but use that water for non drinking purposes and use a filter if you're worried. Filter only needs to be attached to inlet filling hose, not plumbed in.
When the tank is new...fill, add one or two boxes of bicarbonate .....and slosh it around ....we usually just tow the van around the block. Let the solution settle then empty and flush the tanks several times. Refill and keep filled unless van is sitting unused for a few months. If you forget, just empty and flush again before departure.
For drinking, carry water you know is safe.. Our approach now is to grab a slab of water from Costco, Coles or such and carry in vehicle. We know that water is fine to drink and is easy to stow in nooks and crannies in the car so is always accessible. We also carry a couple of empty 20 litre containers and fill with water we're happy with if we're staying for a few days. We also have a water testing kit...marine use..which is easy to use so that lives in the van.
So....the bicarbonate will take the taste of a new plastic tank away
The water in the tanks in the van can be used for washing up, showering etc etc
You always have good safe drinking water
And you haven't spent a fortune...
But we sometimes forget to use our drinking water for making ice blocks and use onboard water. What the hell, no problem so far and I'd rather have my scotch at the end of the day with ice.