Chagigah 20A

מדלא קתני בהו מעלה.

It is deduced from the fact that it is not taught in their regard that those who eat non-sacred produce according to the level of ritual purity required for sacrificial food must treat the produce with a higher standard with regard to their degree of purity, like those who actually partake of sacrificial food.

ודלמא האי דלא קתני בהו מעלה, דאי דמו לתרומה ⁠— הא תני תרומה, ואי דמו לחולין ⁠— הא תני לחולין. דתנן: חולין שנעשו על טהרת הקודש ⁠— הרי הן כחולין, רבי אלעזר ברבי צדוק אומר: הרי הן כתרומה.

The Talmud asks: But perhaps the reason for this fact, that a higher standard is not taught with regard to those who actually partake of sacrificial food, is that these foods are not on a distinct level of ritual purity, as, if they are similar to the level of teruma, teruma has already been taught; and if they are similar to non-sacred produce, non-sacred produce has also already been taught. As we learned in a baraita that they are not considered to be on a level of their own: Non-sacred foods prepared according to the level of ritual purity required for sacrificial food are like non-sacred food; R' Elazar, son of R' Tzadok, says: They are like teruma, but not like sacrificial food. Therefore, the fact that this level is not explicitly mentioned affords no proof.

אלא מסיפא: יוסי בן יועזר היה חסיד שבכהונה, והיתה מטפחתו מדרס לקודש. יוחנן בן גודגדא היה אוכל על טהרת הקודש כל ימיו, והיתה מטפחתו מדרס לחטאת.

Rather, the proof is derived from the last clause in the Mishnah: Yosei ben Yo’ezer was the most pious member of the priesthood, and yet his cloth was considered impure by the treading of a zav for those who ate sacrificial food. Yoḥanan ben Gudgeda would eat non-sacred foods prepared according to the level of ritual purity required for sacrificial food all his days, and nevertheless his cloth was considered rendered impure by the treading of a zav for those preparing the purification waters.