Re- Question 70 on what is one supposed to do after the seder with the wine from the Kos Shel Eliyahu, where we mentioned that Nitei Gavriel (Pesach 2: 101: n.21) quotes that Horav Yaakov Landau zt’l related that R.S.B. of Lubavitch zt’l would pour the remainder back into the bottle, after adding a bit of wine to the cup, (for non-pogum purposes).
Q. I cannot understand the reasoning of the 4th opinion of adding wine to the cup, for non-pogum purposes. Nobody has drunk from the cup. Therefore, the cup is not pogum. Unless they are giving credence to the idea that we were told as children, that Eliyahu HaNavi sips from the cup when he slipped in unnoticed during Shefoch. In that case it would be necessary to pour in a bit of wine before Kiddush in the morning according to the 2nd opinion and
before the drinking of the 4th cup according to the 3rd opinion.

A. Horav Shlomo Miller Shlit’a mentioned that others do not have the tradition of Kos Shel Eliahu at all. He added that another widespread minhag, (also quoted in Nitei Gavriel, ibid.) is to pour a bit of the wine in the Kos Shel Eliahu into the fourth cup of all present. It is therefore conceivable that in the process, someone including children, may have also tested the wine directly from Eliahu’s cup.
Additionally, Kaf Hachaim (186: 21) opines that introducing a finger into the wine also makes it pogum, (other Poskim disagree).
The Rov added that since the Kos Shel Eliahu may remain uncovered an extended period of time, and Mishna Berura (272: 3) maintains that if wine is left uncovered more than a “sha’a muettes” (a short time) one should on the onset replace it when possible for kiddush use . Adding a bit of wine to the Kos may also be helpful. (Magid Teshuvo O.H.: 15, opines that adding wine may according to some Poskim, also be a tikun for yain megule).

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a