I usually pressure wash it real good and throw it into a trash can full of water with some big stones to hold it down. I check occasionally and when it sinks I take it out and blast it with the pressure washer once more. Sometimes I will do a few water changes on the bucket of it looks funky or smells.
Depends, I had a log about as round as my forearm that took 5 or 6 months.
Also be sure to check out: the endall driftwood " thread