From: Rabbi Moshe Sofer
To: Rabbi Avraham Yitzchak Weinberger
The Chasam Sofer rules leniently that an animal whose kidney was found filled with clear but salty water is kosher. He demonstrates through careful analysis of Talmudic and halachic sources that the category of 'clear water' permitting the kidney was never defined so as to exclude salty water, and that the stringency regarding salty water in lung blisters pertains to the definition of a blister, not to the kidney laws.
Source: Shu"t Chasam Sofer YD §47