U-shaped pipe made of copper, used in plumbing and HVAC systems to prevent sewer gases from entering a space by trapping a small amount of water. The "P" shape is created by the bend and the horizontal pipe that connects to the main drainage line. In HVAC, it is also sometimes installed on refrigerant lines to keep the compressor primed with oil, particularly when it is over 30 feet long. Need larger quantities? Contact us for bulk pricing and availability.