Ok I've done this a few times and this is what works the best imo. Even the most sunbleached most dry driftwood. First, inspect it. Investigate splits to make sure there's no rot. You'll know if you see any. Then what we did was put it in our spare bathtub with lightly salted water. The salt kind of sterilizes it to an extent while it also speeds waterlogging. This can take awhile but soak it until it sinks. When it sinks replace with fresh dechlorinated water and soak about three more days. Even if it is still a little bouyent you can hold it down with a heavy rock until it stays down. Best wishes!