I don't know if it works with all materials but in recent years I've come across a trick that "works a treat" (Without the Mudcat that is not a phrase I would ever have used. *g*).

I dump some dishwashing liquid in the bottom and fill it with water (I've used both hot and cold water with equal efficacy) to the brim of the traumatized stuff and set it back out of the way. A day or so later I dump it out and lo!