You're on the right track, but I would soak the wood a while longer; throw out the old water and replace it with fresh tapwater every hour or so to get rid of the bleach that has already soaked out.

Another method for disinfecting driftwood is to boil it in a pot of water; if the piece is too large for a pot you can just pour boiling water on it. This way you don't have to worry about bleach residue.