An Empty Bottle is a small, glass container for holding potions and poison. Bottles can either be empty or filled with a potion. If a bottle is empty or filled with poison, you can hold as many as you can carry. But if it contains a potion mixture, only 20 of each potion can be held.
Those who practice alchemy need bottles to put their potions in. You can recycle bottles; drinking a potion always leaves another empty bottle behind. These are usually given to clerics and druids so that more potions can be mixed. Practitioners of poisoning will also need empty bottles to craft bottles of poison, but these bottles are not recyclable (perhaps owing to the dangerous poison residue).