Mithrandir has studied the artifact that Ayorzén stole from the vault of Durthang and believes that if it might be cleansed of its corruption it could be empowered with a force for Good.
'I have studied the artifact that Ayorzén stole from the vault of Durthang. It bears a powerful corruption, but it was not made in the land of Mordor. It came from elsewhere, and the corruption that envelops it stems from its long stay in the Black Land. If this evil could be cleansed, I believe that Elrond could imbue it with a powerful and vital force for Good.
'Before that can happen, however, we must do something about the corruption that Mordor has worked upon it. There are different methods to accomplish this, though the Wise disagree upon the effectiveness of each. My preferred means for such a cure is to bring the corrupted item to the place where it was made, or to places of some significance upon its path, and to thereby diffuse the foul touch of Mordor that has, in the interim, claimed it. We must learn the story of this heirloom before it came to Mordor.'
The Wizard turns the artifact over in his hands, studying it for some clue to its origin. To your eye the heirloom is a small and mostly featureless cup. Then you see that a single blood-red ruby is mounted on one face of the cup, and you marvel that no enterprising Orc in Mordor ever sought to remove the valuable gem. Mithrandir seems to know your thought.
'Yes, the stone is precious, but that is not what has caught my eye. This cup is very plain, otherwise, but the clay from which it was fashioned is of a type that was oft-used among the hill-men that populated Rhudaur during the days of that kingdom's ascension. Elrond may know more, for the Last Homely House is hidden not far from the reaches of old Rhudaur. Yes, speak to Elrond, and learn what he may know of this heirloom of Rhudaur.'
Elrond can be found in the library of the Last Homely House, in Rivendell.
The course of the Bruinen in the Misty Mountains falls in three levels before it comes out of the mountains.
Elrond asked you to fill the cup of Rhudaur with cold, clear water from waterfalls in the Misty Mountains, and to defeat any creatures drawn by its corruption.
Elrond is in his library in Rivendell, waiting to advise you about your journey to the Lost Temple to cleanse the cup of Rhudaur.
Elrond is at the Haven of Orladion in Rivendell, north-west of the Last Homely House.
You have cleansed the corruption from the Cup of Sacrifice and should bring it now to Elrond in Rivendell.