All potion phys-reps must be large enough to hold at least a minimum of a quarter ounce of liquid. The phys rep does not actually have to contain any liquid to be valid.
To use a potion, you must role-play the proper drinking motions, and this must take at least three seconds. You should not count it out loud. Only one potion may be quaffed at a time.
A potion may be “force fed” to an unconscious or sleeping person by someone else, but such a character cannot “accidentally” drink one. You cannot attach a potion or elixir to your collar or shield and “bite” into it to get its effects while bound or in battle. You must be able to actually hold one in your hand, motion removing a cork or cap, and then mime drinking it.
Potions cannot be mixed into food or drink or diluted or mixed together in any way. If multiple are poured into the same container, both potions are ruined and provide no effects when consumed.
Earth Potions always have an implied Spell qualifier, just like an incanted spell.
All potions affect the drinker only, and bypass any protective spells such as Spell Shield or Reflect Spell. They can, however, be resisted by applicable racial abilities (such as Resist Spell or Resist Necromancy for a Necromantic potion).