An earthenware vessel protects all [substances from becoming tamei], according to the opinion of Beis Hillel. But Beis Shammai say: It protects only foods, liquids and earthenware vessels [from becoming tamei]. Beis Hillel said to [Beis Shammai]: Why? Beis Shammai said to them: Because it is tamei through the am haaretz, and a vessel which is tamei cannot interpose. Beis Hil-lel replied to Beis Shammai: But have you not de-clared tahor the foods and liquids that are in it?! Beis Shammai replied to them: When we declared tahor the foods and liquids that are in it, it was [only] in regard to [the am haaretz] himself that we declared [them] tahor. But if you will declare tahor the vessel, you will have declared it tahor [both] with regard to you [the chaver] and to him [the am haaretz]. And Beis Hillel reversed [themselves] to [thenceforth] rule in accordance with the opinion of Beis Shammai.

R' Chanina, administrator of the Kohanim testified [concerning] four matters: In all the days of the Kohanim, never did they re-frain from burning [sacrificial] meat that had been contaminated by a derived tumah together with [sacrificial] meat that had been contaminated by an av hatumah, although [by doing so] they added tumah to its tumah.  R' Akiva added: In all the days of the Kohanim, never did they refrain from lighting oil that had become disqualified through a tevul yom in a lamp that had been contaminated by one who was tamei from a corpse, although [by doing so] they increased its tumah.