I suspected as much. In any case, we wait for the diagram.
Actually, I should not leave it at that. Calling "that" a conjunction is a cop out. "That" is different. Sometimes linguists refer to the decay of the cases or gender, or something like that, referring to the way that languages have tended over time to become more simple. I believe that the same may be true for descriptive grammar. "That" is not like "other" conjunctions. Consider "dass" in German. But, if "that" so used must have a quick title, as a dictionary would tend to give, "conjunction" is not bad.
But... the diagram?
The cop out is "function word". "Conjunction" is a perfectly reasonable name for a word that conjoins two things.