I've four rabbits all are still caged because not fixed yet so they are completely separated from each other and I trained them to use their toilet and we have good results especially with my males, Leo is 7 months and Fred was a rescue so can't be sure but think he's about 1 year old now. They are both very tidy rabbits and like their floor clear just moving everything into corners so the middle is always free. Leo's cage has a bit slippery floor at the moment so I gave him a shallow cardboard tray filled with hay it is normally on his left side so he still has a little space to stretch on the floor between his toilet and this tray because he likes laying on his plastic floor maybe it's too hot on hay. I just pushed both trays close together so they'd fit into my camera.
Here you can see Leo's cage after 4 days after changing his toilet box. He'd easily survive a week without changing it but it's summer and I usually just remove this little corner pee-spot and move some wood pellets into that corner, and fully change litter once a week. As you can see there's no hay in his toilet after 4 days so literally no hay wasted at all. When he had his hay manger above his toilet it was always very messy he'd pull all the hay down and mix with pellets and pee on it it was very stinky and lots of wasted hay as well.
Fred has similar setup his toilet absolutely same after 4 days just his favourite pee-spot is opposite closer to the door, and because his cage's floor is structured and not slippery he doesn't need extra coverage for the floor and his hay is just under his bench which is on the opposite side from his toilet. This way they never have hay in their toilet boxes.
My girls are a bit different, they both like their floor covered with hay and they would drop some berries on it, so I usually give them a feeder stuffed with hay but they would pull it out by the evening and cover their floor with it so I just lift the hay every day or every other day and remove the berries and put hay back, they usually don't pee outside their boxes. When they had hangers over their toilets was the same story and toilet box was full of messy stinky hay after a few hours after cleaning. Now I change their litter every 3 days but Bernie drinks a lot more so her litter is full sooner so every two days especially in summer, but she'd survive 3-4 days if really needed.
I will try to take pics of my girls cages later when I am home but this Leo's toilet I took photo last night before cleaning, well I just removed this pee-spot and left it for another 3-4 days.
So, I find that keeping hay separately from toilet boxes really works for my rabbits, I don't waste much now.
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