This procedure has never failed me, what i do instead of boiling i have a 5 gallon bucket that i use
1 run the hot water in your tub till it gets the hottest that it can get and fill the bucket, drop in the bogwood and let it soak over night, in the morning when you wake up, pour out the cooled off water and do the same thing over again, go to work or school or whatever, when you come home scrub the bogwood in the water you have it in, pour it out and rinse the bogwood off.
Takes me one day, from start to finish and i have never had any tannen released, no discoloration at all.