Sea sponges are simple marine animals of the phylum Porifera, which consists of several species that occasionally wash up on beaches. Sponges lack a nervous system, and they are composed of network of collagen fibres and "ostia" (open channels that allow food, water and debris to flow to the animal's interior). The animal is covered with a thin skin that often remains even after it has washed ashore. The process of cleaning sea sponges is relatively simple and involves the removal of this outer skin, leaving the porous skeleton behind. These cleaned sponges are often collected by hobbyists or used as home decor.
Dampen a piece of burlap with water, and cover the sponge. Leave your sponge under the burlap for several days, or until the outer skin has rotted off. You might want to place the sponge outside during this time because it will smell.
Put on a pair of rubber gloves, and rinse the sponge under running water. Squeeze the sponge to remove any non-skeletal debris that might still be inside.
Fill a container with rubbing alcohol, and place the sponge inside. Close the lid to the container, and let it sit for 48 hours.
Remove the sponge from the alcohol, and place it in a sunny spot to dry completely. The cleaned sponge will be a light colour, full of open pores, and will lack any remnants of the dark outer skin.
Store your sponge in a dry environment to preserve it.
Always use care when handling sea sponges, and never squeeze them with bare hands.