Wine glasses of a gentile-Using glass vessels of a gentile that were used to drink or store Yayin Nesech:
No need to Kasher with hot water: It is permitted to drink from clean wine glasses, and other clean wine glass vessels, of a gentile without Kashering them in between [using hot water] even if they were used to drink and store Yayin Nesech. This applies even for Ashkenazim. [This applies even if one lent the wine glasses to a gentile.] However, at times the Shichshuch form of Kashering is required, as will be explained.
Washing out the cup prior to use: Prior to using the wine glasses, one must make sure to rinse the vessel so there is no leftover wine left in the cup.
Shichshuch-When is it required? In the event that one desires to use the vessel on a permanent basis, such as if one purchased used wine glasses from a gentile, then one must Kasher the vessel prior to its use through the method called Shichshuch. Likewise, if one desires to drink wine from the vessel, even one time on a temporary basis, it requires Shichshuch prior to its use. However, if one desires to use the wine vessel for non-wine beverages on a temporary basis, then Shichshuch is not required, and it may be used after a good rinse, as stated above. [This allowance for temporary use of non-wine beverages applies to all vessels of a Gentile irrelevant of material and whether it was used for storage.] The definition of temporary use is as follows: Temporary use refers to using it only on a necessary occasion, such as one is in the home of a gentile and does not have another cup available, or has another cup available but has a preference to use that specific cup. It is forbidden, however, to use the glass cup on a steady basis, unless Shichshuch is performed, as explained above.
What is Shichshuch-Rinsing well with water three times: The Shichshuch method of Kashering is accomplished in the following way: Prior to using the wine glasses, one must make sure to wash the vessels out very well with water. Likewise, one must rinse the vessel a total of three times prior to using it. If one did not rinse out the cup three times prior to its use [i.e. Shichshuch], then it may not be used in any case explained above that Shichshuch is required [i.e. for wine, or for permanent use].
Bedieved if one used the cup without first performing Shichshuch: If one used the cup for wine prior to rinsing it out three times [i.e. Shichshuch] as required, then according to some opinions, the wine is forbidden even Bedieved. Practically, however, one may be lenient to permit the drink Bedieved [so long as it was rinsed from any leftover wine prior to its use]. This applies even the wine remained in the cup for 24 hours. Certainly, if one used the cup for non-wine beverages, according to all opinions the beverages are permitted to be drunk Bedieved, even if Shichshuch was required beforehand [such as if one is using it permanently]. This law applies by all material wine vessels that only need Shichshuch for their Kashering, and not only to glass vessels.
Drinking non-wine beverages: It is permitted on temporary occasion to drink any non-wine beverage from a vessel of a Gentile even if the vessel was designated for drinking or storing wine, so long as the vessel is properly rinsed from any leftover wine prior to usage. If one desires to use the vessel on a permanent basis, then it is required to be rinsed well three times prior to its use even for use of non-wine beverages.
Drinking wine: It is forbidden to drink wine from a glass vessel of a Gentile that was used to drink or store wine, until it is rinsed well three times.
Practical Q&A-Coming up in part 2
 However, at times, Shichshuch is required, as will be explained.
 Not a problem by any vessel unless wine is stored in it for a while [i.e. 72 hours-Chochmas Adam 81:3]: Michaber Y.D. 135:1 based on Avoda Zara 33b and Rashba Toras Habayis Hakatzar 5 10:64; By glass is not a problem even if stored in it for a while: Michaber 135:8; Darkei Teshuvah 135:3 in name of Kehal Yehuda
 M”A 451:48 “Although we are stringent by Chametz, do not compare it to Yayin Nesech, as many leniencies apply by Yayin Nesech”; Rama ibid omits writing any gloss on this statement of Michaber ibid, and so is implied from Shach Y.D. 135:23 and Taz 135:11 who both comment on this ruling and explain that glass is smooth and does not absorb.
 See Michaber and Rama 136:1 that vessels designated for wine require a Chosem and otherwise need to be Kashered; However, see Shach 136:3 that the entire stringency here is because it’s as if he entered it for storage, and hence since by glass we are lenient even if it is entered for storage, therefore it does not need to be Kashered.
 Michaber Y.D. 135:1 and 137:4
 See Shach 137:16 on Michaber 137:4 that even if one plans to use it for non-wine beverages, it may not be used “Derech Keva” until it is properly Kashered, as rules Rama 121:5 regarding all non-Kosher vessels, and the proper Kashering for a glass vessel is Shichshuch, as rules Michaber 135:1; See Imrei Eish Y.D. 44; Darkei Teshuvah 137:11
The reason: As one may come to use the cup with wine, which will absorb the taste of the Yayin Nesech and become forbidden. [See Shach 137:15-16]
Other opinions: Some Poskim rule that one may drink non-wine beverages from the cup on an even permanent basis without Kasheirng it beforehand. [Kneses Hagedola 137:23; Chochmas Adam 81:12; See Imrei Eish Y.D. 44; Darkei Teshuvah 137:11]
 Michaber 135:1 [regarding general rule] and Michaber 137:4 that the allowance to use without Shichshuch is only by non-wine beverages; See Shach 137:15-16
The reason: As the Yayin Nesech wine taste absorbed in the cup gives taste to the wine, and is not nullified in it even in 100x. [See Shach 137:15-16]
 Michaber 137:4 regarding non-wine beverages that only a mere rinse is required; Shach 137:16 that this applies only for temporary basis use
The reason: As the taste of the Yayin Nesech in the cup is nullified within the non-wine beverage. [Shach 137:15]
 See Michaber 137:4
 Admur 451:2 “On occasion”; 450:13; Rama Y.D. 121:5 “Temporarily, such as for example..”; Shach 91:3; P”M 91 S.D. 3
 Rama ibid
 Implication of Admur ibid; See Piskeiy Admur Yoreh Deah 91 p. 122
Background and other opinions: The Rama in Yoreh Deah 121:5 rules that it may only be used “Temporarily, such as for example if one is in the home of a gentile.” This implies that only if one has no other vessels available may he use it, and not that it may be used once in a while even if other vessels are available, and so rules the Yad Yehuda 91 Aruch 4 and 8. This, however, is not the simple understanding from the words of Admur who seems to imply that the vessel may be used on occasion even if other vessels are Kosher available. [See Piskeiy Admur Yoreh Deah 91 p. 122]
 Michaber Y.D. 135:1
 Michaber Y.D. 135:11; Tur 135; Rabbeinu Tam in Tosafus Avoda Zara 33a; Divrei Yosef 3:907; Darkei Teshuvah 135:3; Shulchan Gavoa 135:2; Hagahos Maharshal 135:1
 Taz 135:14 in implication of Rabbeinu Tam ibid and in his understanding of Rama 135:11; So also writes Taz 137:1 in name of Rama
 Conclusion of Taz 135:14 and 137:1 that by all vessels which only need Hadacha [i.e. Shichshuch] one may be lenient Bedieved if it was not done
 Taz 137:1
 Yad Yitzchak 1:96 that so applies even according to Shach ibid; Darkei Teshuvah ibid