What way do the men at the campfire provide for Montag to escape from the Mechanical Hound?

The men at the campfire give Montag a bottle of something to drink which is designed to change his body chemistry, so that the composition of his sweat and his personal "smell" will be different from what the Hound is looking for. He literally will not smell like Montag any more.

He turned into a different person after drinking the liquid