My six year old son is very smart and articulate. ?

He never is any trouble at school and always scores the highest possible points in his clroom everyday, but he is lazy. I know this is kind of gross, but he is afraid to wipe himself properly after, please excuse my french, a bm. He'll go around for at least an hour until someone detects the smell and complains. I always throw away his underwear and make him take a shower. It's starting to get so bad that it occurs almost 5 times a day. I buy a new pack of undies for him every week. And the water bill is way higher. Any suggestions?