Zevachim 73A

כל דבר שיש בו מנין ⁠– אפילו בדרבנן לא בטיל, וכל שכן בדאורייתא.

Any item that is counted, even if it is prohibited by rabbinic law, e.g., teruma of fruit, cannot be nullified, and all the more so items prohibited by Torah law, such as animals that are disqualified for the altar, as in the Mishnah.

דתניא: ליטרא קציעות שדרסה על פי עיגול, ואינו יודע באיזו עיגול דרסה; על פי חבית, ואינו יודע באיזו חבית דרסה; על פי כוורת, ואינו יודע באיזו כוורת דרסה –

This is as it is taught in a baraita (Tosefta, Terumot 5:11): The baraita discusses 3 cases, all of which relate to the tithing of figs, which is an obligation by rabbinic law. The first is the case of a litra of untithed dried figs that were pressed in different vessels and shaped into circles, that one placed into a jug containing tithed figs, and during the process of producing a circle he pressed the figs onto the opening of one of the circular vessels in which the circles are formed, and he does not know into which circular vessel he pressed it. The second is the case in which he recalls that he pressed it on the opening of a jug containing tithed figs, but he does not know into which jug he pressed it. The third case is that he recalls that he pressed it on the opening of a straw receptacle containing tithed figs, but he does not know into which receptacle he pressed it. In all of these cases, there is a dispute between R' Meir and R' Yehuda as to the details of a dispute between R' Eliezer and R' Yehoshua.

רבי מאיר אומר, רבי אליעזר אומר: רואין את העליונות כאילו הן פרודות, והתחתונות מעלות את העליונות.

R' Meir says that R' Eliezer says: One views the upper layers of possibly untithed dried figs as though they are separate pieces, rather than one unit. And the lower ones, which were there beforehand and have certainly been tithed, nullify the upper ones, as there are enough circles of figs to nullify the upper layer. One does not need to tithe the figs at the top of any of the containers.