“Pigs” are inserted into the pipe to clean it out. When the pigs eventuallyexit the far end of the pipe clean, then the line will be filled with dry air. Air compressors pump up the air, and the air is run thru a drier. A pig may discharge from the pipeline with considerable velocity and force. The pig catcher is a basket at the end of the line to safely receive or catch the pig when it discharges from the pipeline.