What should not be connected to plumbing systems that do not allow drainage?

Connecting plumbing systems that do not allow drainage to certain components can lead to serious issues. Drum traps, while able to contain water and prevent sewer gases from entering a building, require a continuous flow of water to function properly. If a drum trap is connected to a drainage system that does not allow for drainage, it can lead to clogging or backflow, undermining the intended functionality of the trap.

In contrast, other components like P-traps or air gaps are designed to serve specific functions that do not depend on constant drainage flow. P-traps, for instance, prevent sewer gas from entering the home while allowing for the occasional drainage. Air gaps provide a physical separation between potable water and non-potable water, helping to avoid contamination but not requiring drainage. Safety valves, such as pressure relief valves, are designed to discharge water or steam to prevent dangerous pressure buildup and do not require a functional drainage system in the same way a drum trap does.

The unique reliance of drum traps on continuous drainage demonstrates why they should not be connected to plumbing systems without that capability, making it critical to understand the limitations and functionalities of different plumbing components.