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."







