If it's fizzing, then your o-ring is probably shot. They need to be replaced reasonably regularly if you're always opening and closing the vent plugs. Good thing they're really cheap.
Even with water in the board, a properly sealing o-ring will not fizz.
As the board cools once on the water, it will be sucking anything around the vent plug into the board

.
Getting water out is a mission, take JayBee's advice and read up on Eva's stuff on the Boardlady site.