If a cat is going to the bathroom throughout the house, first have him checked by your veterinarian to make sure that he doesn't have a urinary tract infection. Once that has been ruled out, try confining the cat to a small area like a bathroom or cat carrier, making certain that the cat has a litter box, food, and water. You can slowly increase the amount of space allowed to the cat once he starts successfully using the litter box. Make sure that you're consistent and, if a mistake occurs, go back a step and repeat the process.