In the early years of the fire service, water lines were made from wood. When there was a fire, the first arriving company would drill down into the water lines to get their water. When they were done they would simply drive a wooden plug into the hole as opposed to replacing the entire section. This is where we get the term "fire plug". During this time there were only volunteers, the first firefighters to put water on the fire were paid by the insurance companies. The competing companies would send the meanest, toughest, biggest, guy they had ahead to guard the plug. Anyone from another company who came near it would have to fight him. This is where the term plug ugly comes from.