Sinks

Question

Is the reason that sinks don't need to be kashered because (A) their rov tashmish is not with hot water/food or because (B) it is noten taam lifgam? If B is correct, what if hot pesach food came into contact with the sink within 24 hours of hot chametz? (I know it sounds a little far fetched, but Torah Hee V'lilmod ani tzarich!) Thank You As Always