I was washing a VERY hot milchig pan and it touched the walls of my metal milchig sink. The question is, when I moved into my apartment, I did not kasher the sinks because my sister-in-law lived there a few weeks before me. She told me it’s milchig. I trust her kashrus, is it okay to rely on the fact that she told me it’s milchig?
Also, the milchig and fleishig sinks are separated by a metal wall, so is that an issue? How should I proceed?
Everything is kosher and fine. You may rely on your sister to tell you that her sink was milchig. If you trust her kashrus, this is included in it. Therefore your milchig pot touched your milchig sink, so there is no problem at all. The metal wall is sufficient to separate the sinks, as long as there is no moisture between the wall and the sinks.