Ken asked: it appears the #10 can shelf are at an angle so they can roll, but the water barrels appear to be level. Is that correct, or are they at a slant also?
No, the barrels aren't slanted like the shelves. Due to the weight of the barrels, I wanted to keep them level to even distribute weight at the support points.
However, in the fully horizontal position, gravity will drain some 85% of the volume of the barrel (or more). At that point the weight of the water will be manageable and you can slide the barrel out and tip it downwards, as shown in the image below.