Pip hid a large amount of food, and Joe thought Pip had swallowed it whole. Joe remarked, "Manners is manners, but your elth's your elth [your health is your health]." Joe is saying that while good table manners are important, health (avoiding the risk of choking) is more important.

He probably means: Your health's your health. Lots of people in England drop the "h"s.