Parashas Metzora · Passuk 15:12
Chabad.org — English translation + Rashi
Torah Temima points to Toras Kohanim.
English: “That he touches” — it is said here “bo” and it is said there “in which it is cooked”: just as there [impurity is] through its airspace, so here through its airspace — and not from its exterior.
Earthenware: airspace only
Chazal apply the standard rule of earthenware vessels: the zav’s impurity affects them through their interior airspace, not from the outside.