For bathtubs and sinks, leave 1 inch of water in them. For only one or two favouritely soiled areas, try feeding the cat at that spot. There are many other creative ways to make a spot aversive to your cat, but they must be used in conjunction with tactics to get him back to the litterbox, for if you train him to avoid one area he will go to another instead. Make sure the food is not too close to the litter. This process may have to be carried out for 2 weeks or more.
Most cats prefer an easily accessible spot, but one with some privacy.
So strike a balance between getting it out of the way for your own sake, and making it private but not too distant for the cat's sake. Some cats prefer open boxes, some prefer the privacy of closed boxes, most like large boxes, a few like small ones. This type of preference can develop very quickly if a cat first chooses to go out of the litterbox for any other reason. It is to be strongly suspected if a cat repeatedly goes back to one area, or one room. To help treat this type of problem, you may actually have to provide a litterbox in the cat's preferred spot to get the cat using the box again, and then slowly move the box back to another location.