As Bearhawker noted above, it is the Crank Tank 4 from Adventure Hydration in Australia. Holds 4L, so when completely filled ends up being enough water for all day during hot weather. During milder weather or when I know there is potable water available during that days riding, I tend it only fill it halfway. It is also nice to fill it before setting up camp because then I have plenty of water for cooking, cleaning and drinking at camp. For refilling it without taking it off, I carry a collapsible water bottle that I can refill at water fountains/spigots/sinks etc, then pour it into the tank with the cap removed. If you look up their website, keep in mind the prices are in Australian dollars, so it's not as expensive as it initially looks. Cheers!