Do you have a pot about 1 foot deep? You can boil it, keep flipping it over and over. The steam and hot water (running down over the exposed side from what was just boiled) will take care of the middle.
Wasn't suggesting to fill the tub with boiling water, just pouring the boiling water (from a pot) onto the wood while it is in the tub. This is how I cure all of my large driftwood
turkey fryer lol, but really a good scubbing with the hottest water you can handle and it''ll be fine some wood just wont sink for months but you can get a slate tile and silicone it down or drill a cple holes in the slate and use stainless steel screws to attach it