Christopher Steele had no first hand knowledge of anything he put in his dossier. The information was mostly supplied by someone referred to as the Primary Sub-Source, someone Steele hired to do the research for him. When the FBI interviewed Steele in October 2016 he refused to reveal the identity of his source.
But in January, the FBI found and interviewed him. The Primary Sub-Source debunked the entire dossier. But the FBI interview team buried that fact for 34-months. The FBI's failure to tell the FISA Court that the main source for the dossier blew a hole in the government's case was one of the most significant errors in the entire investigation.