What time is the last bus of Beijing Airport and where it stops ?

Sorry but I am still confused. You replied earlier that it stops at Xidan Aviation Building. When I phoned the Airport, a man in charge told me the last bus stop at Beijing Train Station but only after the last domestic arrival. The lonely planet guideboook mentioned last bus from the airport is Line 3 and after the last arrival(international and domestic).
Kindly confirm again which shuttle bus line from the airport is the last; and is it only after the last domestic arrival or all arrivals; so that I can book my hotel room nearer to the stop.
Thank you.