You might start by suggesting that Squealer could be represented by a sponge. It starts out small, but grows much larger as liquid is added and absorbed - certainly Squealer, as did all the pigs, grew fatter and fatter through the course of the story.
Perhaps Squealer could be represented by a pencil eraser. He was an expert at changing things, explaining the rewritten version of the commandments of Animalism, rewriting the history of the revolution.
Squealer could be represented by a coin. He changed his story or his position as he needed to in order to meet changing situations, as easily as turning a coin from heads to tails.
Squealer could be represented by waxed paper. All the stories he told and all the reasons for events that he gave early in the story, he disowned by the end of the story. The earlier versions rolled off his back like water running off a piece of waxed paper.
Squealer could be represented by vegetable oil. He was slick and got into lots of things.