A Nochri siphone some wine from a tiny hole in the barrel, why this would assur the remaining wine in the barrel if there was no physical contact with the rest of the wine in the barrel. (through his mouth? or becuase of chances of liquid being pushed back into the barrel?)
Shabtai Nacson, Toronto, Canada
The Ran explains that the case of drinking with a straw forbids the entire barrel as all of the wine in the barrel becomes a base for the wine which is being drawn through the straw. He compares this to the case of Tvul Yom brought later (60a, see Rashi there DH "Nikvah mi'Piha").
All the best,