When communing during the Divine Liturgy of the Presanctified Gifts, the celebrant clergy (Priests and Deacons) receive the Holy Body and Precious Blood via the intincted Lamb that is placed into their hands, which is the Body of Christ already intincted with His Precious Blood at the previous Divine Liturgy of St Basil the Great. The chalice is then partaken of by only those clergy who will not consume the Holy Gifts at the end of the service; that is to say, the Deacon (if one be present) does not partake of the chalice at this point, or if no Deacon serves, the junior Priest if multiple Priests serve without a Deacon; or, if a single Priest serves alone, he does not partake of the chalice after he has communed of the Holy Gifts, but only at the end of the service, after he has consumed the remainder of the Lamb at the Table of Oblation, and purifies the vessels.
Those who do receive of the chalice at the time of communion, after already having communed of both the Body and Blood of the Saviour from the intincted Lamb, do so silently, without the words that normally accompany partaking of the Precious Blood from the chalice at the Divine Liturgy of St John or St Basil.
Explanation: While it is abundantly clear that, once the portion of the intincted Lamb that contains the Precious Blood is placed into the chalice after the fraction of the Lamb at ‘The Presanctified Holy Things are for the holy…’, the Blood therein commingles with the wine and the water poured into the chalice, the tradition of the Church does not proclaim that this wine and water thereby become the Lord’s Precious Blood simply by contact with the Blood from the Lamb (despite the fact that certain Fathers have pondered on this). For this reason, though it is treated with scrupulous piety and care, we do not partake of the chalice as if it contained solely the Precious Blood of the Saviour, but wine and water also, offered in memorial of the full Liturgy at which the Lamb was consecrated and sanctified, now touching and mingling with that Blood even as we have just done so ourselves in partaking of the Lamb, and nourishing us at the breaking of the Eucharistic fast, having just been strengthened with the Holy Mysteries.
The cleric (or clerics) who will consume the remaining Holy Gifts at the end of the service do not partake of the chalice at the time of communion, so as not to break the Eucharistic fast before their reception is complete.
This is the living tradition of our Church as it has been handed down to us; it is to be kept without fail in all our parishes, irrespective of what might be discussed in other contexts or found printed in other books or rubrics.