Apologies, the source is wikipedia's page on Paul Manafort[1]. Also the article says he was involved with Yanukovich, not with Putin, but still in the worst case this is in the equivalent to the Biden-Poroshenko tape[2].
Tax fraud rendering you guilty of all the bad things you were ever accused of is not really sound logic. Also, I am not really defending Manaford - tbh after reading more on him, this whole Ukrainian foray seems to be one of his lesser offenses. But for example in the case of Flynn/Trump where prosecutors were taped discussing how they need to "find him guilty of anything or provoke him to cross the law", there is no doubt of bias.