Rule reminder
'Quanto' as a relative pronoun means 'tutto quello che' (everything that / all that). It is used when the antecedent is a whole idea or unspecified amount, not a specific noun. Example: 'Dimmi quanto sai' = Tell me all you know. It can also appear in formal expressions like 'in quanto' and 'per quanto'.
Ti dico ___ so sulla faccenda.