[willy]

best at this point would be to open up the hole as said, let it drain out whatever in there, sitting h0ot in sun would probably help. The best way is to apply suction of some kind and see what you can draw out. Go to a mariners shop and find out the name of a product that hardens rotting wood. There is a commercial version sort of like a git rot product but better, it hardens like an epoxy. let it set up as per instructions, then fill with an two part epoxy or a 5200 and let it set up.
That is what a fellow I met years ago told me. He said he used and air pump of some type, I believe an air compressor set up for it and drew out a couple of pints out of the wood thru a little hole.