Great Expectations

Chapter 5 was really confusing for me because I didn't understand where Pip and Joe were going with the sergent and his men. I re-read the passage and I think they are hunting for the escaped convicts in the marshes, but I am not sure. I also didn't understand what they were talking about before they left. Pip states, "The sergent took a polite leave of the ladies, and parted from Mr. Pumblechook as from a comrade; though I doubt if he were quite as a fully sensible of that gentleman's merits under arid conditions, as when something moist was going." This stiflingly formal diction is hard to process and I did not understand what Pip meant when he said this. Please answer my question and help me better understand this passage.