Please allow us to store clean herbs inside of the herb sack.

Even if you can only store one or the other at any given time (grimy or clean), it would still make sense lore-wise without being a coding nightmare.

Try to store grimy herbs in a sack of clean herbs? "Putting these in the sack would ruin the clean herbs already inside of it."

Try to store clean herbs in a sack of grimy herbs? "You don't want to ruin your clean herbs by mixing them in with a sack filled with dirty ones."