Travelling from Peking airport to Tianjin after midnight

Hi, I live in Tianjin and I have to receive a friend flying in next month. He will be landing at the Capital airport around 11pm. So assuming it takes 1hr for customs/baggage clearance, it will be past midnight by the time he gets out. I'm wondering how to get back at that time, because the shuttle bus, airport express and the rails all start after 6am. I've heard that the slow train is available from the West station after midnight, but am not sure how to get there or about the timings. Can anyone give me some details? Thanks