Soaked both of mine for some time in a bucket just enough to hold it down in the tank and just got away with water changes to clear up the tank.
My first piece however was placed in when I was cycling my tank and due to the increased temperature you have the tank at for the optimal bacterial soup I got away nicely with a mostly soaked out log come the end of the cycle.
It varies though, my much larger and 2 piece took around 2 weeks of soaking and 2/3 weeks of being jammed down using the hood in my tank to finally sink.