No, my cat has never been caught drinking from the toilet, although she never really gets the chance as the lid is always down to keep her from ever trying it. She does, however, like to sit on the lid and bat blindly at the top of the tank. I say 'blindly' because she has this weird habit of tilting her head so she is looking out of only one eye at the subject and then, having lost her depth perception, she will try to bat at the lid with her paw and usually ends up swatting at the air. It's the oddest thing to watch because I know her eyes work just fine, but she's acting like she's half blind or something. Also, my cat is not a chewer, but one of her sisters is. Her real name is Miranda, but we all call her the Shredder. She firmly believes that her job around the house is to destroy any piece of paper or cardboard that falls to the floor, and proceeds to do so. She helped me open my birthday presents one year, but she only opened one gift before she lost interest and found something else to do. It's possible that your cat simply likes the feel of cardboard in his mouth. It squishes a little bit when he bites it, and perhaps that is where his interest lies. Some cats will chew power cords for the same reason, because they're squishy. As far as drinking out of the toilet is concerned... cats often like to choose their own 'stuff' and this includes not only toys but also food and water dishes as well. It could be that he simply doesn't like the water dish he's been given and this is his way of telling you. Or, if he drinks a lot, he could have diabetes, which has symptoms similar to that of humans. Make sure that he is healthy, for one thing, and also check to make sure his water dish is full at all times. My cat has two water bowls at all times, but usually only drinks from the one, simply because she likes the looks of it and no other reason. I hope some of this helps you out.
