Train from Beijin South Railway to Tanggu

I want to get from Beijing South Railway Station to Tanggu during the day. Is the best way to purchase a ticket from Beijing South Railway to Tianjin, and then Tianjin to Tanggu. And if so, how much time should I give myself for the transfer? i.e. if the Tianjin to Tanggu train leaves at 11:12am, should I arrive Tianjin approx. 30 mins, or more or less - so I can find the right platform without being too rush??