How long does a potion last?

[An Enemy Spy]

I'm running an encounter in my next session where an enemy is going to have a potion of Sanctuary. In the spells section, it says the duration of a Sanctuary spell is 1 round/caster level, but I don't know what the caster level is for a potion.

[Allanimal]

Unless otherwise specified, potions, wands and scrolls use the minimum caster level that can actually cast the spell.
Sanctuary is a 1st Level cleric spell, so CL =1

Edit: it is possible to make the potion with a higher caster level - just adjust the pricing based on the formula in the DMG.

[Grand Poobah]

I'm running an encounter in my next session where an enemy is going to have a potion of Sanctuary. In the spells section, it says the duration of a Sanctuary spell is 1 round/caster level, but I don't know what the caster level is for a potion.

Typically it’s the minimum level required to cast the spell. In your example it would typically last 1 round. You could make the casters level higher but that usually increases crafting costs, which may or may not be an issue for you. In that case, make the CL whatever you want.

Edit: Ninja’d.

[An Enemy Spy]

One round doesn't seem worth the effort of taking the potion.

[Allanimal]

One round doesn't seem worth the effort of taking the potion.

Indeed. If you are the DM, you can increase the CL to get a longer duration. This increases the cost of the potion, so consider this when gearing up the NPC.

[Eldariel]

One round doesn't seem worth the effort of taking the potion.

Which raises the question of if such Potions would exist in the first place. Probably CL5 at least, with the appropriate price increase.

[Doctor Awkward]

One round doesn't seem worth the effort of taking the potion.

The effect isn't worth taking the potion either.

Per the magic item rules, the default saving throw for an effect produced by a magic item (http://www.d20srd.org/srd/magicItems/magicItemBasics.htm#savingThrowsAgainstMagicItemPo wers) is 10+ the level of the spell + the modifier of the minimum ability score necessary to cast the spell.

A 1st level spell requires an 11 to prepare and cast. Thus the saving throw against a sanctuary effect from a potion would the a DC 11 Will.

[An Enemy Spy]

Does raising the CL affect the DC or is it a flat 11 no matter what?

[MesiDoomstalker]

Does raising the CL affect the DC or is it a flat 11 no matter what?

Flat 11. If a magic item provides a save, it will nearly always be so small and insignificant that it might as well not exist.

[Biggus]

Does raising the CL affect the DC or is it a flat 11 no matter what?

The only way to increase it would be to make the potion at a higher spell level using Heighten Spell.

[HouseRules]

Unless otherwise specified, potions, wands and scrolls use the minimum caster level that can actually cast the spell.
Sanctuary is a 1st Level cleric spell, so CL =1

Edit: it is possible to make the potion with a higher caster level - just adjust the pricing based on the formula in the DMG.

Ur-Priest means Minimum Caster Level = Spell Level.

[Doctor Awkward]

Does raising the CL affect the DC or is it a flat 11 no matter what?

Aside from the Heighten Spell metamagic feat which was already mentioned, the only way I know of is the Enhance Item feat from the Epic Level Handbook, pg. 114.

Despite the source, it is explicitly by the text not an epic feat. It allows you to choose any one item creation feat that you know and, when creating items using that feat, use your character's ability score modifier to determine the save DC for any effects rather than the modifier of the minimum ability score necessary to cast the spell embedded in the item.

[Biggus]

Aside from the Heighten Spell metamagic feat which was already mentioned, the only way I know of is the Enhance Item feat from the Epic Level Handbook, pg. 114.

Despite the source, it is explicitly by the text not an epic feat. It allows you to choose any one item creation feat that you know and, when creating items using that feat, use your character's ability score modifier to determine the save DC for any effects rather than the modifier of the minimum ability score necessary to cast the spell embedded in the item.

Oh well remembered, I'd totally forgotten that existed.