It is not as difficult as you think to teach your cat to use the toilet!!!
1. Gradually move your cat's litter box nearer to the toilet until finally it should be next to the toilet. Ensure that your cat is always comfortable and sure of its litter box's location.
2. Now start elevating the cat's litter box. Put something non-slippery like newspapers or cardboard underneath the litter box. A normal rate to increase the height of the litter box would be about 5cm a day, but be very attentive to signs that your cat is not comfortable with the current height, and adjust the pace of raising the litter box accordingly. The cat litter box should be raised until it is at a level height with the toilet bowl. Throughout this process it is very important to keep the toilet lid open and the seat down, because your cat will get used to it and might even start climbing on the toilet seat in order to reach its litter box.
3. Move the litter box to rest on the open toilet seat. Keep it there until your cat seems comfortable with this arrangement.
4. Buy a metal bowl or tray that will fit snugly inside the toilet bowl. It would be advisable for the metal bowl to have small draining holes. Fill the bowl with cat litter (preferably the flushable type). Now remove your cat's litter box entirely. If you have reached this step successfully you are very close to having a toilet trained cat!
If you are having problems finding a bowl or tray that will fit into your toilet you have the choice of buying a complete system such as Kwitter Litter. Further down the page is a video demonstrating this system
5. While your cat is using the metal bowl inside the toilet, be attentive to where its paws are. The goal is teaching him to squat with all four paws on the toilet seat rim. You can move the cat while it is using the toilet and praise it (or reward it) when it is sitting in the correct position. Normally the cat will first sit entirely inside the metal bowl, then with front paws on the toilet seat, and finally it should sit with all four paws on the toilet.
6. Start using less and less cat litter. This can get smelly, so be sure to clean the bowl after every time your cat uses it. Cats scratch in sand or cat litter to cover up the smell (this is out of instinct), so if the bowl becomes too smelly your cat won't be comfortable using it (and you probably wouldn't be comfortable with using your toilet either). Using flushable cat litter makes cleaning the bowl very easy - just throw out the contents in the toilet and flush down, rinse out the bowl, refill with correct amount of cat litter and replace. A handy tip is to place newspaper on the floor around the toilet to help keep the room clean should your cat scratch in the cat litter. Decrease the amount of cat litter in a pace that your cat feels comfortable with.
7. When you basically don't use any cat litter inside the bowl anymore, start gradually filling the bowl with water. The water will also help mask the smell so your cat will be more comfortable using the toilet. Be attentive to your cat's behavior through this whole process - if your cat stops using the bowl inside the toilet, you may be moving on too fast and might need to go back a couple of steps.
8. When the water level in the bowl has reached about 4cm and your cat has no problem using it, it is time to remove the bowl entirely. Your cat should now be toilet trained. Remember to always leave the toilet seat up and flush regularly!
For more info go to http://www.catsofaustralia.com/cat-toilet.htm