You only need to scrape off the dirt on the outer skin with a knife, no need to soak it! Best to wash in warm water! I used to use a soldering iron to burn it red in the fire, then burn it on the dirty outer skin until it was black, then scrape off the black skin with a knife, and finally wash it with warm water several times until it was clean! I also did this when I was a kid. I did this on pig heads and feet. The skin on pig tongue is the dirtiest