From Beijing to cruise port in Tianjin, Do you go from Beijing to Tanggu or direct to Tianjin

I was told to go to Tanggu from Beijing, then by taxi to the International Cruise Home Port in Tianjin. On further checking I can't find trains to Tanggu. Is this correct or do I go directly by train to Tianjin. Also is it possible to purchase the tickets in the vending machines at the South station