Cleaning Aquaroll

Newbie first mistake, eager to go on my first trip in a weeks’ time, needed to get Aquaroll and wastemaster, bought second hand and although in great condition on the outside so assumed it had been used for clean water, got home and it looks a bit grubby inside, it does not smell but doesn’t look like it’s been used for clean water.

Although not bought for drinking water I will use bottled water for that, it’s just hand washing and showering etc., I would still like to see it spick an span inside, could I chlorinate it and then flush out or can you advise a better method.