Which type of trap should not be installed in a drainage system?

The bell trap is not recommended for installation in a drainage system primarily due to its design, which can lead to issues with maintaining a proper water seal. A bell trap is shaped like a bell and typically becomes prone to trapping debris and sediment within its body, which can result in blockages. Additionally, its design may not effectively prevent sewer gases from escaping into the living space, which goes against safety standards and health regulations outlined in the plumbing code.

In contrast, P-traps, S-traps, and wye traps have designs that facilitate proper drainage while maintaining a water seal to prevent the ingress of sewer gases. P-traps are common in household plumbing, particularly under sinks, due to their ability to catch debris while ensuring that a sufficient water seal is maintained. S-traps, while somewhat outdated in certain applications, can still be effective in vertical runs of drainage. Wye traps, though specialized, also serve a useful function in drainage systems when installed correctly.

By focusing on the specifics of various trap designs, it becomes clear why the bell trap is less desirable in contemporary plumbing systems compared to the alternatives.