Question for Catholics about Biblical Interpretation

[John 6:29]

I've heard many Catholics ask the question to Protestants, "How do you know what the Bible says? There's thousands of Protestant churches, so obviously none agree on what the Bible says." They use this as an argument to show we have to have the "true Church" explain it to us within the means of tradition. They also use this argument for a refutation to one of the sola's of the Reformation, Sola Scritpura.

But, suppose we need the "true Church" to explain us what the Bible means. Say we need the tradition of the early Church fathers to explain it to us. Still, these leaves us with an issue. How do you know that you are interpreting the tradition of the early Church Fathers appropriately? Even if someone directly tells you what the Church Fathers meant by saying something, that person had to interpret the writings of the Church fathers, so you are still left with what you call a private interpretation of the Bible. So, how do you know you're interpreting and understanding what you are taught, outside of the Bible, correctly? Even if the Pope, or a Priest, tells you something. You still are left to interpret what that Pope or Priest is telling you, thus you're still left to your own interpretation.