I usually fill a pot with water, put the wood in (weight it down with a spoon or tongs or something if it won’t sink) and boil for at least an hour. Occasionally, I turn the wood with some tongs if it is possible to rotate it. Beforehand, I give the wood a good scrub if it needs it to remove dirt.
I haven’t had any issues with just boiling once, but you can do it again if needed.
Do you still get the water discolored with one boil