I know that some food products come in 5-gallon buckets. I've seen a bunch of them at the Costco bakery for making muffins, bagels, bread, etc. I'm not sure if they toss them in the trash, recycle them, or if there's a reverse logistics chain to take them back to the supplier to be cleaned and refilled. If it's one of the first two you might be able to get a bunch for free,