If one will be staying in a non-Jewish home, may he use their glass cups? Must he kasher them? For hot versus cold?
If the glasses are clean, they may be used for cold. Regarding using them for hot foods, the minhag of the sefardim is that they don’t need to be kashered. Even according to the Ashkenazim that are stringent regarding glass, however glasses are usually only used as a kli sheini, therefore they should preferably be kashered. Pouring hot water over them should be enough.
O:CH 451-25. There is controversy among the Ashkenazi Poskim if glass can be kashered or not. In our case that it was only used for a kli sheini, we can be lenient, and therefore hagalah of a kli sheini would be enough.