Water closets shall be computed as ____ fixture units when determining septic tank size.

In plumbing design, the calculation of fixture units is essential for sizing components like septic tanks. Water closets, commonly known as toilets, are typically assigned a value based on their water consumption and expected usage.

The correct answer indicates that water closets should be computed as 6 fixture units. This figure is used because it reflects the average potential demand and loading on the septic system that a water closet generates, making it a crucial factor in the design and sizing of the septic tank.

Assigning 6 fixture units ensures that the septic system can handle the flow and waste generated by the water closet, offering a buffer for peak usage times and ensuring adequate treatment and capacity. This approach helps prevent overloading the system, which can lead to failures or backups, maintaining overall sanitation and effectiveness in waste management. Properly computing fixture units is a key aspect of ensuring a well-designed and functional septic system.