What is required for every trap and trap fixture in plumbing systems?

Every trap and trap fixture in plumbing systems must be vented. Venting is essential because it provides air to the drainage system, ensuring that the water in the trap does not siphon out when wastewater flows through. This maintains the trap's water seal, which is crucial for preventing sewer gases from entering living spaces.

Venting allows for equalization of pressure in the drainage system, facilitating proper drainage and preventing the water in the trap from being pulled down due to negative pressure created by the flow of wastewater. Without adequate venting, the trap could lose its water seal, which serves as a barrier against odors and harmful gases.

While cleanouts are important for maintenance and access to the drainage system, they are not a requirement for every trap. Insulation is generally not necessary for traps, and traps should not be larger than the pipes they connect to in order to function effectively. Thus, venting is the critical requirement for every trap and trap fixture in plumbing systems.