It is not clear if this was the common practice amongst all the priests serving at the tabernacle, or if only the sons of Eli did this. The context suggests that Eli’s sons are in view seeing as they are specifically identified in 1 Samuel 2:12 and 1 Samuel 2:17.1
13 The custom of the priests with the people was that when any man offered sacrifice, the priest’s servant would come, while the meat was boiling, with a three-pronged fork in his hand,