Consider the following scenario: A person is invited to a house which uses cholov akum, He is offered a hot drink (without cholov akum) in a cup that has been used for hot drinks with cholov akum. May he use this cup? According to the Maharsha (Gilayon Maharsha, Shulchan Aruch, Yoreh Deah, beginning of 113) cholov akum does not make a keli sheni forbidden.    There are however Poskim who disagree with the Maharsha. I might add that nearly 50 years ago when I did a course on kashrus given by Rav Getsel Ellinson, he told us, and I have it written down in my detailed notes from the course, that cholov akum does not make a keli sheni forbidden.

I recollect from about 40 years ago, when I lived in England, kosher butter arrived from Holland which was only supervised “mishas asiya”, namely that the milk it was made from was cholov akum, yet people who would only drink cholov yisroel would use such butter. The reason is that milk from non-kosher animals cannot be made into butter. (Schach, Yoreh Deah 115:27)  Such butter is however only permitted if one obtains already made butter, but should one make cholov akum into butter, the butter would not be permitted. (Rema, Shulchan Aruch, Yoreh Deah 115:1)

About 50 years ago, whilst I was living in an area of London, there was a certain occasion when there was a problem to receive cholov yisroel. Rav Morris Swift z’tl who was then a Dayan on the London Beis Din also lived in the same area, and he related to us that the milkman thought that for milk to be cholov yisroel, a Rabbi had to bless it. He therefore went to this Rav and said “You are a Rabbi. Will you bless the milk?!”

I heard that during the Gulf War (1990-91) when Jewish soldiers were stationed in Saudi Arabia, the question was asked whether they could rely on Rav Moshe Feinstein’s heter for cholov akum. The answer given was they could not, since unlike in the United States where all the milk is cow’s milk, in Saudi Arabia there was also camel’s milk.