Fill a 32-gallon plastic garbage can or plastic tub two-thirds full of lukewarm water. Place the rawhide skin in the container, submerging as much of it as possible. Push the rawhide down further into the water as its bottom softens, working until the entire piece sits in the water. Place a brick on top of the rawhide if needed to keep it submerged completely. Leave the rawhide to soak for one to 12 hours, until its entire surface becomes pliable.