Final answer:
The S-trap is no longer used in residential construction due to safety concerns related to sewer gas entry and siphoning of the trap seal. It has been replaced by the more reliable P-trap.
Step-by-step explanation:
The type of trap that is no longer used in residential construction is a. S-trap. The S-trap is outdated and has been replaced by the P-trap, which helps prevent sewer gases from entering the home. The S-trap design was prone to siphoning the trap seal, which could allow these gases to enter. Additionally, modern plumbing codes typically prohibit the use of S-traps due to these safety concerns. Instead, P-traps are now the standard in residential plumbing because they maintain a constant water seal and are less prone to siphoning.