I have soaked mine in a large tub more than once - for about 20-30 minutes each time. I used warm water and about a cup of white vinegar. I scrubbed it with a shower scrubber while it was soaking to get the "hairs" out.
I took it out and laid it flat on a towel on the floor and dried it.
I had no problems. It is still flat as can be. Soaking isn't a miracle, and it isn't a new board, but it did help a little bit. If nothing else, it was clean. :)