Perhaps you misunderstood.
After the chalice is purified -- the remaining Precious Blood is consumed and the chalice is washed with water which is also consumed -- the chalice would be washed well and that water is poured in the sacrarium.
This is from Redemptionis Sacramentum (bolding is mine):
[107.] In accordance with what is laid down by the canons, “one who throws away the consecrated species or takes them away or keeps them for a sacrilegious purpose, incurs a latae sententiae excommunication reserved to the Apostolic See; a cleric, moreover, may be punished by another penalty, not excluding dismissal from the clerical state”. To be regarded as pertaining to this case is any action that is voluntarily and gravely disrespectful of the sacred species. Anyone, therefore, who acts contrary to these norms, for example casting the sacred species into the sacrarium or in an unworthy place or on the ground, incurs the penalties laid down. Furthermore all will remember that once the distribution of Holy Communion during the celebration of Mass has been completed, the prescriptions of the Roman Missal are to be observed, and **in particular, whatever may remain of the Blood of Christ must be entirely and immediately consumed by the Priest or by another minister, **according to the norms, while the consecrated hosts that are left are to be consumed by the Priest at the altar or carried to the place for the reservation of the Eucharist.