I attempted to toilet train a cat I had. It was going really well. But he started peeing in the bathtub instead. Come to find out...he had leukemia and had started to shows symptoms at that time. I really think had he not gotten sick, it would have worked out well.
As far as not going potty where the cat goes...just think of how gross it is that your cat steps all in its pee and poo in a litter box. Then it walks all over your furniture and probably your kitchen counters. Then it comes and sits on you. Ew! 4951