As far as I know residue covered pots are nasty for ever, with no way of fixing it. This isn't really a huge issue and yet I would love to see the player being able to wash the pot with soap and water.
Maybe you would full the pot full of water and let it boil for a bit (to make stuff that doesn't want to come off be looser), and then in the crafting grid you could craft it with soap to make it a soapy pot. Then you would rinse it off by chunking it in a pond or something.
That's all, thanks!