Commentary for Avodah Zarah 74:4
ושמואל אמר דכן מלטמא אחרים אבל טומאת עצמן יש בהן קסבר טומאת משקין דאורייתא לטמא אחרים דרבנן וכי גזרו רבנן במשקין דעלמא במשקין בי מטבחיא לא גזרו:
But Shmuel said that it was pure in the sense that it did not render other things impure but in itself there was impurity. He holds that the impurity of liquids is from the Torah; but with respect to its power to render other things unclean it was a rabbinic ordinance, and when the Rabbis decreed, they decreed it about liquids in general, but they did not decree it about liquids in the slaughter house.
Daf Shevui to Avodah Zarah
Shmuel holds that this liquid is susceptible to impurity, but that even if impure, it does not convey impurity to anything else. This is unlike liquids in general which are highly conducive of impurity. Liquid impurity is from the Torah, but it is only the rabbis that hold that it can convey impurity to other things.
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