A Revit MEP system family that routes fluids - water, drainage, gas - between plumbing fixtures and mechanical equipment. Like ducts, pipes connect through connectors and auto-generate fittings as a run is drawn, but also carry a pipe system type (domestic hot water, sanitary, storm) that governs slope requirements and connection rules. Sanitary and storm systems typically need a minimum slope, which Revit can flag automatically if a run falls outside it.