Which plumbing concept describes the collective responsibility for multiple facilities connected to a sewer?

The concept that describes the collective responsibility for multiple facilities connected to a sewer is best represented by a "Common Waste System." A Common Waste System indicates a unified approach where various entities, such as commercial buildings or residential blocks, share a single wastewater system that connects to the main sewer line. This shared responsibility ensures that maintenance, management, and regulatory compliance are collaborative efforts among the connected facilities.

In contrast, "Public Drainage" typically refers to the municipal responsibility for water runoff and stormwater management, while "Private Sewer" usually denotes a sewer system owned and maintained by a single property owner. A "Shared Sewer Network" could imply a decentralized approach, but it lacks the specificity and regulatory framework often associated with a common system for waste management. Thus, "Common Waste System" is the most accurate descriptor for the scenario presented in the question.