What type of fittings are prohibited when using cast-iron for drainage?

Screwed fittings are prohibited when using cast iron for drainage due to the inherent properties of the material and the nature of the drainage systems. Cast iron is typically utilized in drainage systems because of its strength, durability, and resistance to corrosion. However, screwing fittings onto cast iron can compromise the integrity of the joints over time.

The threads can weaken the structure of the cast iron, leading to potential leaks or failures, especially under high-pressure conditions. This is particularly concerning in drainage applications where maintaining a watertight seal is critical. The use of glued, welded, or flanged fittings, which provide a stronger and more reliable connection, is favored in drainage systems using cast iron.

By using appropriate fittings that ensure secure joints without compromising the material properties, plumbing systems can operate more efficiently and last longer without the risk associated with less compatible connection types like screwed fittings.