usually, the heat & moisture go to the attic from the fan, then should circulate inside the attic, another fan up in you roof and the eavestrough will carry those air in and out, make your attic breathable, now if the out side temperature below 0, then those moisture will condensate and become ice, and cumulate around your ceiling 排风扇周围, when the temperature go above 0, (or your heat is TOO high, ), the ice will melted , and the water no where to go, causing leak.—nothing to do with the 黑色塑料管子—that should be for the 下水管出气口