What is the reason for the prohibition of drinking from the mouth of the waterskin?

The questioner: It means in the container.

The Shaykh: May Allah guide you.

The questioner: If he pours it, meaning there is no harm in that.
The student: The topic is finished, O Shaykh.

The Shaykh: The important thing is that he does not put his mouth on the mouth of the waterskin, for it will become foul-smelling.

The questioner: ... Our Shaykh, now ... I mean, the reason, as I see it or hear it from you, is only that germs adhere to this skin, so what is inside it becomes foul-smelling. Now, if we put something inside the waterskin, like water, will the water become foul-smelling?

The Shaykh: ... Of course.

The questioner: It becomes foul-smelling?

The Shaykh: Of course, its taste will change.

The questioner: Yes, so whatever is put in the waterskin.

The Shaykh: Allow me a moment, because you are expanding too much on the hypotheticals here. I said if we put something, what is the thing you want to put? What will be in the waterskin? It will be water.

The questioner: Water or milk.

The Shaykh: What is the thing you want to put?

The questioner: I am rambling around an issue that is not my main point, O Shaykh.

The Shaykh : If Allah wills.

The questioner: I mean, this is the question.

The Shaykh: Give your attention to the main point, it will be in the manner of Abu Ayyub.

The questioner: No, no.

The Shaykh: And it will be in another manner.

The questioner: I am not Abu Ayyub.
The student : ... .
Another student : Our topic is finished now, O Shaykh.

The Shaykh : Yes, praise be to Allah.
The student: It is in the archive.

The questioner: Fine, good, I am done, I understood this issue.

The Shaykh : Praise be to Allah.

The questioner: Yes, it remains.

The questioner : The Sunnah.

The Shaykh: The eager one who raises his hand is fidgeting to the right and left, as if he is fleeing from it, my brother, his turn is coming.