"Seems these guys would go around and distribute large pots (kinda like their vinegar pots) for free, then come around a couple times a week to collect the deposits, and give the folks a few cents for the trouble of using their service. These guys would then truk the carts down to the river, and load up boats of the pots, or fill larger onboard tanks. These boats would then haul the contents back out to the distributed farms, to the happy farmers, who would happily give a buck for the high quality fertilizer. Salaries would be distributed back up the tract, and everyone was happy."
I've had this kind of idea, but for like an urban/suburban composting type program.