Use your thumbnail, nothing harder, to break through the build-up after soaking for an hour or so in the bathtub. Then just wash with a wash cloth in a soapy solution. Rinse well, let the cork dry, then hit it with some 150 grit to take off the top layer of slime that remains on the cork.

I rinse my rod every hour or so while out fishing, usually after baiting up and cleaning the egg slime off of my hands. Just takes a second and it avoids the build-up problem in the future.