I used a little insentive to train DS. He wanted a fire engine in the shop. It stayed there for about a year (he spotted it when he was around 2) and finally one day he said i want that fire engine inthe shop. "well" I said, "you have to do all your poos in the toilet". By the end of the week he decided for himself that he wanted the fire engine enough to do his poos on the toilet.
For wees I let him run around in the nude....boys think it is great watching themselves do wees, and they get to have a play too