What must every trap and trap fixture be?

Every trap and trap fixture must be vented to ensure proper drainage and to prevent the buildup of sewer gases within the plumbing system. Venting allows air to enter the system, which eliminates vacuum formation that can disrupt flow, leading to slow drainage or backups. It also helps to regulate the pressure in the plumbing system, ensuring that traps retain their water seals. A trap that is not vented could lose its water seal due to the differential pressure from the drainage system, allowing sewer gases to escape into the living space, which poses a health risk. Thus, proper venting is crucial for the functionality and safety of plumbing systems.