Understand the drying takes the moisture out of the wood and it may take years on some species, so when we want it to sink we have to remember that the water has to find it's ways back into lots of those tiny holes in the cellulose. Takes time, even years, so we need to speed it up.
Lots of different ways to do that. Some easy, if the right tools are on hand, some hard.
One way to speed up soaking is to boil but that is tough with big wood. Another way to open those cells up quicker is too move the water further into the wood by drilling or cutting. a big piece that you know which sides will be hidden can sink pretty quick if you drill a bunch of holes in the hidden side to let the water in as it also reduces the amount to float.
One large hole filled with gravel and sealed with silicone is a quick way.
I most often use a piece of slate or other soft tile and screw it on as it lets me choose what angle and which side up much easier. For getting the tile, I like the really expensive stuff that has large holes as it is easy to drill but I do a fair amount of it and give it out around the area, so I have found that dealers almost always have leftovers, broken or other tile stacked around in back and often are open to letting you sort the pile for free. Just talk nice and say thank you?