The story of Fang Lang owing money for his passage sounds like a family legend. He travelled with seven other Chinese firemen on ticket 1601, which was paid for by the Donaldson Line. He was going to join a small ship called Annetta, which used to operate in the Caribbean. (The name of the ship is given as Anetta in the US inquiry, but my version is from Lloyd's Register).
More positively, Tom provides a source for the story of Fang Lang being rescued after floating on wreckage. This incident is in several books but I've never seen a primary source. If this is documented by a contemporary letter or newspaper report, it would clear up another loose end.