It is not possible to clean between the glass of a double-paned window without professional help. If condensation builds up between the two panes of glass, it means the seal is broken somewhere on the window and must be repaired to prevent the foggy appearance.
Silica dessicant can be inserted between the panes through the leak to help absorb the moisture for a temporary fix. When a window repair professional is called, he drills a hole in the window frame and pumps a cleaning solution inside. The moisture is sucked out and a defogging device is used to dry the window completely. The window is then repaired.