Ashkenazi people In a situation where a Pyrex dish was used to cook both meat and milk in frequently (not together obviously)
The food have been treif?
The kli shenis made of cheres be treif?
And could you kasher the Pyrex dish?
A pyrex dish (Ashkenazi minhag) according to many poskim is considered like glass, (except regarding hilchos Pesach). It should prefferably not be used for both milk and meat even seperately, firstly because it is controversial is this is peritted or not. Secondy, from a practical angle, if it is used for both types and will eventually get mixed up, or it will not be washed out well etc. and it can cause problems. In retrospect though, the food will not treif, and then everything after it will also be permitted. Regarding kashering it, it can be kashered in a kli rishon.
Bais Lechem Yehuda 121-10, Eliyahu Rabba O:CH 87-2, MInchas Yitzchok 10- 85(12), Maharsham 3-94, Darcei Teshuva 121-2 in the name of a number of Achronim that the Rema only meant to be stringent ragrding hilchos Pesach, Igros Moshe O:CH 5-32-1, Mishne Halachos 9-168, Halichos Even Yisroel 45, Hilchos Basar B’chalav inthe name of R’ C. Kanievsky, R E. Auerbach, and R T. weber shlit”a, Haichos Shlomo chap. 3 ftnt. 76.