Final answer:
The correct option 1) is a trap, which is essential for indirect waste piping requiring an air gap to properly discharge into the building drainage system, ensuring sanitation and public health.
Step-by-step explanation:
The correct answer is option 1) a trap. Indirect waste piping is designed to prevent contamination between the waste water and any consumable water, which could occur if there was a direct connection. An air gap ensures that there is no direct connection between the waste piping and the sanitary drainage system by introducing a physical separation between the end of the waste pipe and the flood level rim of the receiving receptacle, usually a sink, floor drain, or other plumbing fixture.
This gap prevents any backflow or siphoning of contaminated water back into clean water areas. After passing through the air gap, the indirect waste must then enter the building drainage system through a trap, which provides a water seal to prevent sewer gases and odors from entering the building.
This is essential for maintaining sanitation and protecting public health, as these measures effectively separate the clean and waste water systems and mitigate the risks similar to the historical incidents such as the Great Stink of 1858 in London.