Boiling only gets most of the tannins out. To water log it you have to soak it in water for quite a few weeks if it’s really dry. If the log is light, it’s not water logged.
Since you got it at the beach you will need to do extra steps to ensure that your not brining contaminants into the tank. You will need to scrub it good and use lots of hot water to kill off any other parasites that might be in the wood that attached itself to the wood.