All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
We are not aware of any authentic evidence that it is a recommended act to eat and drink from the same vessel. However, it is confirmed that the Prophet used to lick his fingers when eating and the vessel he ate from. Indeed Imaam Muslim reported that the Prophet recommended that we lick our fingers and vessel and said: "You do not know where the blessing is."
It might be that the brothers did what the questioner described seeking the blessing. If the water is poured in the vessel and then people drink from it, then it brings with it the remaining food in the vessel.
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Allaah Knows best.