Originally Posted by Mogurako
Boil it for a few hours, or attach it to a rock. I typically just let it float for a week or so and it eventually sinks.
Don't boil it, boil hot water and pour over it, I think the air pockets explode when you boil it. I had heavy rocks sitting on mine for 2 weeks before putting it in the tank, and three months later, it floats happily alone. :/