Yogurt works great, better than milk (adult cats are milk intolerant, so while you can give them milk once in a while without (many) consequences, it's likely milk will make the stool very loose, even to the point of diarrhea). The salt method has been suggested to me, but I haven't tried it.

One of my cats is an absolute maniac about water. It has to be just out the tap, and he has to see you changing the bowl, or he won't drink. For hours if you don't comply. Will call you, scratch, make all kind of pitiful noises until you give up.

He had FUS a few years ago, and we tried first with the special food.