if you have a paper or any sort of pulp cone and a non-treated foam surround i would stay away from putting any amount of water or liquid material on it.
if it is treated with a water resistant material or it is got plastic, metal or anything that on the cone, wipe away.
if you do have a paper with foam, you can clean it with a damp *VERY LITTLE* water rag or paper towel. and let it dry out quickly. you dont want the cone to soak up any water and loose its compression.