Nice find! I have several of those for rainwater storage, and they work great. One word of caution - you'll want to cover it or paint the plastic container if you can. The plastic is quite translucent, so if it sits in the sun uncovered, it will quickly become algae soup. Then it's a pain in the butt to clean out because it clings to every surface inside, and you only have that one six-inch hole in the top to access the inside of the container.
I've got mine wrapped with a canvas tarp, which seems to do a pretty good job of minimizing the algae growth. The cover will also help extend the life of the plastic parts, which will eventually get brittle and break down if they get a lot of direct UV exposure in the sun.