What is the smallest plastic drain that can accommodate a water closet (W/C)?

The smallest plastic drain that can accommodate a water closet (W/C) is 3 inches in diameter. This size is specifically designed to handle the waste and water flow from a toilet, ensuring that it can move both solids and liquids efficiently without clogging.

Using a drain smaller than 3 inches could potentially lead to drainage issues due to insufficient capacity to manage the volume of water and waste generated during toilet use. A 2-inch drain is commonly used for sinks or showers, where the waste is usually liquid and does not require as much clearance as that of a toilet. Options such as 4 inches and 6 inches are larger than necessary for a standard water closet application, which can lead to higher material costs and more complex installation without providing additional benefits for this specific use case. Thus, 3 inches is considered the appropriate minimum size for effective operation.