If it's from a store, I wouldn't do anything but give it a quick scrub in the sink to remove any dust etc and plonk it in! That's all I do with store bought wood and *touch wood* (ha!) hasn't caused an issue yet!
Do not boil wood, it breaks the fibers apart faster and the wood can rot in the tank. Rinse it off under the hot water tap, use a softish brush. It seems to be dry and from the colour I suspect it is going to float until water logged, so you will either have to weigh it down somehow or soak it in a container of water until it is water logged and will sink.
Never soak it in anything other than fresh water, like tap water. Wood absorbs (or is this adsorbs?) substances in the water, and these can leech out later and cause issues, depending. The chlorine in tap water is not an issue.
I'm not sure what wood type it is, some don't release that many tannins though It isn't mopani wood at least, which tends to release a lot. You'll find out when you soak it anyway.
Some of them take a few weeks to waterlog properly so don't be surprised if it doesn't sink within a few days. I've never tied or drilled wood to sink it, sometimes just wedging it down with stones works.
In the olden days pieces like that would often come with flat piece of slate affixed to the bottom - a hole drilled thru the slate and a ss or brass screw spun into the wood.
So that would be one way to do it
Adsorption and absorption mean quite different things.
Absorption is where a liquid is soaked up into something like a sponge, cloth or filter paper. The liquid is completely absorbed into the absorbent material.
Adsorption refers to individual molecules, atoms or ions gathering on surfaces. The surface of a material is made up of atoms and bonds that are exposed to the air. For example, the surface of a piece of glass will be covered in silicon and oxygen atoms. Molecules or ions can interact with this surface via intermolecular interactions. This allows them to ‘stick’, or adsorb, to the surface. If a material has a very high surface area, then lots of molecules can stick to the surface.