What do you think of these? http://www.ebay.co.uk/itm/20L-Litre-Collapsible-Camping-Water-Carrier-Container-/190716690084?pt=LH_DefaultDomain_3&hash=item2c6799bea4&_uhb=1 I used to use solid plastic 25l barrels to fill backpack before I installed my tank. But these could be great for anyone short of space or using a car etc. One empty they'll take up no space at all! Your thoughts?