When the Iron Flask is unstoppered, the owner can command one of the demons to come our for up to 8 hours or until slain (at which point the demon goes back into the flask). During its time of freedom, the owner of the flask controls all actions of the demon. No demon can be called forth more than once per week.
More demons can be added to the flask. The target demon must be within 30 feet, and the owner of the flask must speak a command word (a standard action) to attempt to imprison it. To overcome the spell resistance of the demon (if any), the owner can make a check using the caster level of the flask (30th). Then the demon must succeed at a Will save (DC 20) or be sucked into the flask. The Iron Flask holds up to one hundred demons. Whenever a new demon is imprisoned, the flask must be unstoppered, and 1d4 other demons attempt to escape from the flask. To thwart each attempted escape, the flask's owner must succeed at a Will saving throw (DC 20 +1 per demon in the flask). If a demon escapes, it turns on the flask's owner and attempts to slay him.
Each time a demon is called from the flask, the owner must succeed at a Will saving throw (DC 20 +1 per previous save against the flask +1 per demon in the flask) or become chaotic evil. Furthermore, each time he must also succeed at a caster level check using the flask's caster level of 30th (DC 10 +1 per previous save per demon in the flask), or the demon called is freed and turns upon the owner of the flask. If the demons from the flask ever slay the owner, they immediately steal his soul and take it to the Abyss to become a larva.
Source: Book of Vile Darkness
I see that child who lay upon her bosom and who bore my name, a man winning his way up in that path of life which once was mine. I see him winning it so well, that my name is made illustrious there by the light of his. I see the blots I threw upon it, faded away. I see him, fore-most of just judges and honoured men, bringing a boy of my name, with a forehead that I know and golden hair, to this place—then fair to look upon, with not a trace of this day's disfigurement—and I hear him tell the child my story, with a tender and a faltering voice.