(NSFW) What is the best way to sterilize a natural sea sponge in order to use as a tampon?

I wanted to use a “sea sponge” as an alternative to tampons during my menses. I see these types of sponges, sometimes called natural sponge tampons are readily available in the UK. However where I am they appear not to be at all. The USA also has not OK’d the sale of sea sponges as tampons as they have not been medically approved.

I did some research and found a lot of women had found natural sea sponges, even in Art Supply stores and were using as a sponge tampon.
Here is my question, since I did buy a regular small sea sponge.

What is the best way to sterilize a natural sea sponge in order to use as a tampon?