The port is at Tianjin, isn't? So, I think you should go back to Tianjin from the Great at the first day and stay in a decent hotel in Tianjin. How about the Tianjin Best Western Hotel in Tanggu? It is withink walking distance from Tanggu Light Rail Station or Tanggu Train Station. You can take bullet train from Beijing South to Tanggu directly after the Great Wall. The next day, you can just take bus or taxi to the port nearby.