(The followup to question didn’t work.) Thank you for your answer to why you add new wine to wine left in the glass (pagum). I was unclear on this but it was very familiar to my friends. Now what is the problem in returning the wine to the bottle. Why would the bottle need tvillah? אבל השאלה היא: איך מותר להחזיר את היין לכלי שאינו טבול

The problem with the wine bottle is if the bottle was manufactured by a gentile. Utensils (made from glass and metal) manufactured by a gentile must be immersed in a mikveh and a Bracha must be said upon the immersion, before use. (There are many more details in regard to earthenware and porcelain for which you should consult again, if necessary) According to most opinions this is a Torah requirement. However, we are not required to empty the utensil after purchase since our intention was to buy the contents of the utensil not the utensil and in most cases the utensil is discarded after use. The utensil becomes then like a throw away plate, cup, or pan which does not require immersion in a mikveh. (See Tevilat Kelim by Rabbi Tzvi Cohen pg.57) However, the question arises what if one wants to pour something back into the utensil. Does this now mean that I want to use it and it is to be considered a dish that I want to keep and this is a new use? This seems to be the question raised in the shiur which you saw. According to Rabbi Shlomo Zalman Oirbach zt"l adopted by Rabbi Tzvi Cohen in his book Tevilat Kelim( pg. 109) , one may return the food to the utensil and in your case the wine. This is because returning the wine to the bottle does not make the use of the bottle a new use, it just shows that the person had no need for the food which was removed and is now returning the food. Chag Sam'each