R. Eleazar said: Liquids have no uncleanness at all [by Scriptural law]; the proof is that Jose b. Jo'ezer of Zeredah testified . . . that the fluids (blood and water) in the [Temple] slaughter-house are clean.
Now if it were Torah law, no exception could have been made! So the impurity, such as it is, must be Rabbinic law.
Come and hear: If blood became unclean and he [the priest] sprinkled it unwittingly, it [the sacrifice] is accepted; if deliberately, it is not accepted?
Now this is interesting, because the Torah makes no accommodation for deliberate or unwitting in this case.
It was Rabbinically [unclean], this not being in accordance with R. Jose b. Jo'ezer of Zeredah.
Or perhaps not – maybe there is a scriptural “out” – the Priest’s headplate, which was supposed to provide a certain kind of atonement on its own:
Come and hear: For what does the headplate propitiate? For the blood, flesh, and the fat which were defiled, whether in ignorance or deliberately, accidentally or intentionally. . .[It was defiled] by Rabbinical law [only], this not being in accordance with Jose b. Jo'ezer of Zeredah.
This statement of Jose b. Jo'ezer of Zeredah comes, by the way, as a testimony during a historic battle for control of the Sanhedrin between R. Gamaliel and R. Joshua. “Traditional” rabbinic laws were examined to determine their validity.