Where does rubber hose on rear differential attach 1999 ford explorer?

On a 1999 Ford Explorer, the rubber hose on the rear differential is typically a vent hose. It doesn't attach *to* the differential itself in the sense of a fluid connection. Instead, it connects to a vent fitting on the differential cover. This fitting is a small, usually threaded, opening on top or on the side of the differential housing, designed to allow air pressure to equalize inside the differential. The hose then routes upward to prevent contaminants from entering the differential. The exact location of the vent fitting will vary slightly depending on the specific rear differential configuration of your Explorer, but it will be on the top or side of the differential housing itself.