Illinois Plumbing Code Practice 2025 – 400 Free Practice Questions to Pass the Exam

The correct answer is that sinks and lavatories must be vented independently due to the specific drainage and venting requirements outlined in the Illinois Plumbing Code. Independent venting is essential for these fixtures to prevent the creation of negative pressure in the drainage system, which could siphon water from traps and introduce sewer gases into the living space.

Sinks and lavatories produce a significant amount of waste and, when used, can create fluctuations in pressure within the drainage system. Inadequate venting can lead to issues such as slow drainage or the inability to maintain proper trap seals, which is critical for preventing odors and sewage gases from entering the building.

While other fixtures like toilets, showers, and bathtubs also require venting, the specific requirement for independent venting is more emphasized for sinks and lavatories because they are often installed in locations that can complicate shared venting systems. This ensures that each sink or lavatory functions optimally, maintaining the hygiene and safety of the plumbing system as mandated by local codes.