All of my rabbits poop in just one corner, and yes the poop can come up thru the wire in just 3 days. My answer is to turn the tray, giving the rabbit a clean corner to fill, before it piles up too much. I also spread it out and add more sawdust over it with my rabbits that are poop machines, or in a cage with multiple rabbits. My trays are about 2 and a half inches deep, so can fill quickly. I try to do one stack a day (six trays) and check others randomly and empty the really dirty ones. I have 30 trays down in the bunny barn, and another twenty in the underdeck rabbitry, no way I can do them all in one day anymore, kills my back. Turning the trays really has been helpful, and it is easier to just scoop out that corner as well.