What type of traps are not permitted because they impede drainage flow?

Drum and S-traps are not permitted because they can create drainage issues due to their design. The S-trap, in particular, is shaped like an "S," which can trap water in its bend and create a suction effect that may lead to slow drainage or blockages. This design can also result in insufficient venting, causing potential backup or overflow risks.

The drum trap is problematic for similar reasons. Its cylindrical shape can collect debris and waste over time, leading to clogs, and it can also impede the flow of water through the drainage system. Proper drainage requires a continuous flow, and traps that do not facilitate this can lead to severe plumbing issues.

In contrast, floor traps, deck traps, and yoke traps are designed with drainage efficiency in mind. Floor and deck traps are typically installed in areas where water accumulation is common, allowing for effective drainage. Yoke traps are used in specific types of venting and plumbing systems and contribute positively to drainage flow. Therefore, the design and operational characteristics of drum and S-traps highlight why they are not permitted in standard plumbing installations.