I just wrote a bit long response in someone else's thread, so I'm copying and pasting it here as well:
When litter training, I keep all soft things like blankets and beds out of the cage. I find that a lot un-litter trained (and some trained) bunnies like to pee on soft things.
I start with one or two litter boxes, and once when dealing with a really difficult pair, one in every corner. My cages are very large, 6 feet by 2.5 feet, so I have lots of room to play with.
I keep a spray bottle of half vinegar and half water handy. I use it to clean the cages and to get rid of any urine smells from the floor. The vinegar actually reacts with the urine, and removes any trace of urine smell. I usually leave the litter boxes smelling like litter boxes, and the floors clean as possible. Any stray poops go into the box.
The biggest trick I found with litter training, is clean, clean, clean and clean some more. Any accidents outside of the box need to be soaked up with tissue/paper-towel and put in the litter box, then the floor sprayed with vinegar mix and wiped clean. When litter training, I am wiping down the floors of my cages upwards of 4 times a day. When ever I go by the cage I check for an accident.
Patience is the next most important thing. It may take more than a month for the bunnies to get it. The last pair I did was an older pair of female bunnies, one was about 9 years old and the other about 6. The 6 year old was spayed but the older one I wasn't comfortable putting her under at 9 years old. And they took forever to litter train, but one day after about a month and a half it was like a light bulb went on, and they got it. After that, they have had the best litter box manners out of any rabbits that I have had.
Being spayed/neutered also makes a huge difference. It reduces their urge to mark their territory which is done with poo and pee.
Having a handful of hay in the litter box also helps. It helps to entice them into the box and to keep them their long enough to go. Its like having a magazine or newspaper in the bathroom. Often times, bunnies will defecate while eating (in one end and out the other...).
If you have any questions, please ask!
--Dawn
