I have been to rides where we are required to pick up everything. Every speck of grain included. This is mainly in Death Valley which is a national monument and the rangers require it. It the natural animals get one grain of oats or a wisp of hay, it will probably ruin the environment for all time. [exaggeration is mine].
Anyway, the ride management has collected checks in advance for the clean up fee. Someone inspects your camp before you leave and if it is clean, you get the check back. If not, they keep it and the hired helpers do the cleaning. In order for this to be effective, you must collect at least $25 or $35. It does work however........Too bad we have had to come to this but it is necessary. At another of our rides the same people always stay over the next day and help pick up the garbage bags and clean. In exchange, they either get 1/2 off or free entries to the next ride.