Tighten the screwcaps on the bottom barrel.
1. Clean the threads and put some water on them to make it easier to tighten.
2. Use some pieces of wood and vice-grip pliers as a screw driver to tighten the screw caps. (The piece of wood in the background is some closet shelf trim. The piece of wood in the foreground is walnut and took about an hour to make with a radial arm saw. They also sell a "bung wrench" which is metal: See the link. A bung wrench is better.)
3. Be sure to tighten it enough so that water won't escape.