Don't want to stick a spanner in the works but.... Here it comes....
Warning About Bleach!
Bleach will destroy organic matter, whether it be the skin or wood.
If using bleach, make sure it is dilute (Very dilute) and do not leave the drift wood in it for too long. Otherwise you may end up finding it crumbles away or just doesn't have the life expectancy required.
Other methods of cleaning Drift-Wood before the Final Cleaning rinse include:
~ Leaving it in you back yard for up to a year (Depending on rainfall and type of wood)
~ Taking it into the Bath/Shower with you over a number of times.