What type of fitting shall be used for a deck pump-out to ensure liquid and vapor tightness?

The correct fitting for a deck pump-out that ensures liquid and vapor tightness is the 1.5-inch internal national pipe thread (NPT). The 1.5-inch size is typically specified for pump-out fittings because it provides adequate flow rates for waste removal and accommodates the necessary hardware for securing the connection, which is essential for maintaining a secure and leak-proof system.

Using an internal NPT fitting enhances the capability of creating a tight seal, which is critical in preventing leaks that can lead to environmental contamination. Proper sealing is vital in marine applications where liquids and vapors must be contained to avoid pollution of surrounding waters.

The choice of 1.5 inches also conforms to industry standards and regulations aimed at ensuring safety and environmental protection. In the context of pump-out systems, this fitting size helps facilitate efficient waste disposal while minimizing the risk of spills or vapors escaping into the atmosphere. Thus, it is tailored to meet both operational requirements and compliance with relevant guidelines.