My kitten bites so hard that each time I'm almost in tears. You must remember that a kitten will bite or swipe its paw when it is scared or otherwise while it is playing. The kitten will need your help to regulate the strength of its bite. Soon it will learn to control its bite. My kitten was taught to use the litter box by the breeder.
Nobody teaches the kitten to use the litter box.
This it does instinctively. It is in the cats nature to dig a hole, defecate and cover it. Regarding your dog, I suggest you keep on taking him for the regular walks. I was surprised to see my cat eating grass. Cats do eat grass.