Just go to th top left corner of mossdeep and go in the house.Vuala!
In Mossdeep clty
when your in the cave where you get ditto (in fossil manics house) go in the cave after you beat the elite 4 then go all the way right
YOU CAN'T GO TO BILL'S HOUSE!
Bill in this game is a woman called "Lanette". She lives near the Meteor Falls, if you go there, you can't miss her house, near two Persim Berry Trees.
go to mossdeep and then you will see a man staring at the sea