Charles Ellicott Commentary Leviticus 6:28

"But the earthen vessel wherein it is boiled shall be broken; and if it be boiled in a brazen vessel, it shall be scoured, and rinsed in water." — Leviticus 6:28 (ASV)

But the earthen vessel. —The earthen vessels used by the Hebrews were unglazed. The ordinary domestic vessels throughout the East remain so to this day. From their porous character, therefore, they would absorb some of the fat juices of the flesh which was boiled in them for the priests to eat. And as the absorbed juices could not be washed out, the inexpensive earthenware was to be broken up. (Leviticus 11:35). During the second Temple the fragments were carefully buried in the ground when there was a large accumulation of them.

And if it is boiled in a brass pot. —Being a solid metal, no juices could sink into it, and any of the most holy flesh that might adhere to it could easily be removed by washing. During the second Temple the scouring was done with hot water, and the rinsing with cold.