In plumbing, what does a 'drainage system' primarily consist of?

A drainage system primarily consists of pipes that carry away waste. This system is designed to remove wastewater from various sources in a building, such as sinks, toilets, and showers, leading it safely to the municipal sewer system or a septic system. The effective functioning of a drainage system is crucial for maintaining sanitary conditions and preventing issues like clogs or backups that can lead to health hazards.

While pipes that deliver water are essential components of plumbing, they are part of the water supply system rather than the drainage system. Air ventilation ducts serve to circulate air and are unrelated to the removal of waste. Water treatment tanks are involved in processing and purifying water but do not constitute a drainage system. Thus, B is the most appropriate choice, as it accurately defines the primary function of a drainage system in plumbing.