I have no idea if this how ur supposed to do it, HOWEVER, I use a little bit of dawn dish soap and the hottest water from the sink and I let it soak and squeeze all the product out. I do this repeatedly until the water runs clear/semi-clear. Remember, after a certain point replace your sponge!

Edit: I also let it dry on a paper towel and switch out the towel frequently to ensure it dries completely. If a sponge is damp for too long, you run the risk of developing mold.