What is the proper angle of sewage drainage pipe?

Horizontal lines 3" in diameter or larger should be as close to 1" in 10 feet ( pitch) as possible so that the flow of the liquid component carries the more solid particles along with it instead of having the fluid drain away quickly leaving the solid (feces) to dry out and clog the pipe . Smaller lines can be the same or larger pitch because there usually is no solid material in them.