A faster way is to boil it, it still takes hours and hours, though. Bogwood is a time consumer.
If it already sinks, and you don't mind your water tinting on account of tannins, boil it just long enough to kill off bacteria and plunk it right in.
I didn't want my water tinting, so I boiled it. My medium size bogwood peices, I boiled for around 10-12 hours each, 4 hour spurts, to get the tannins out. Add water, boil for about 30, pour, add water boil for about 30, pour.