These glass vials are held within stylized cold-iron casings etched with strange runes, necromantic designs, or other eldritch markings. Within the vial roils a small wisp of white vapor, churning as if caught in a miniature vortex of air.
To capture a haunt’s energies within a haunt siphon, you need only twist the metal casing to open the vial in the same round that the haunt manifests (a standard action)—this can be before or after the haunt has acted. You must be within the haunt’s area of influence to use a haunt siphon. When you activate a haunt siphon, it deals 3d6 points of positive energy damage to a single haunt. If it deals enough damage to the haunt to reduce the haunt’s hit points to 0, the mist inside the haunt siphon glows green—if it does not reduce the haunt to 0 hit points, the haunt siphon is still expended and becomes nonmagical. It may take multiple haunt siphons to destroy powerful haunts. A haunt that is neutralized by a haunt siphon takes a –5 penalty on its caster level check to manifest again after its reset time passes.
A haunt siphon that neutralizes a haunt can no longer be used to harm haunts, but it can be used as a grenadelike splash weapon that deals 1d6 points of negative energy damage with a direct hit. Every creature within 5 feet of the point where the haunt siphon hits takes 1 point of negative energy damage from the splash.
Complete SRD page: Haunt Siphon