Use bleach /water in a ratio of 1/7 (one part bleach to 7 parts water. Soak it for 24 hours, rinse well and then LET DRY. Bleach breaks down to salt and water, and is harmless once it dries. Having two filter socks would be best, that way you can run one in the sump, while cleaning the other.
Please note that you should ONLY use Plain Bleach, Not products like Tilex or Clorox Clean-up that contain bleach AND surfactants. Personally I wouldn't use scented bleaches, just plain old bleach in the blue/white bottle.