I just don't get how cleaning my sinuses through the endoscopy will fix the sinus? If I do have a fistula, will they be able to see it?

I have an appointment with an oral surgeon the 17th of December. I have not been able to show a recording of the pus coming out to an oral surgeon yet because all the other times I went to one I didn't have one. It was only when I started to get frustrated that they were saying it wasn't coming from my gum that I decided to record it. Hopefully when I take the recording to this oral surgeon it will change their approach to the problem, which has been nonchalant.

In addition to that, I plan to ask him if the endoscopy is good way to proceed with the problem if he comes up with no solutions.