Which type of traps is not permitted in plumbing?

S-traps are not permitted in plumbing systems primarily due to the potential for siphoning. An S-trap has a configuration that resembles the letter "S," which allows wastewater to flow down while creating a trap seal. However, the design can lead to issues where the water seal can be siphoned away during drainage, creating a pathway for sewer gases to enter the living space, which poses a health risk.

Plumbing codes have evolved to promote the use of trap designs that prevent such siphoning phenomena. For instance, P-traps and U-traps are specifically designed to maintain a water seal that effectively prevents the escape of sewer gases while providing adequate drainage capacity. Studor vents are also acceptable as they enable airflow to prevent vacuum formation in the drainage system while maintaining a proper trap seal.

Therefore, the absence of S-traps in modern plumbing practice aligns with the goal of ensuring effective drainage while maintaining proper hygiene and safety standards in plumbing systems.