What is the minimum diameter of a combined house drain or house sewer?

The minimum diameter of a combined house drain or house sewer being 4 inches aligns with most plumbing codes and standards. This size is sufficient to accommodate the necessary wastewater flow from typical household fixtures, such as sinks, toilets, and showers. A diameter of 4 inches ensures that the system can handle the volume of water and waste produced without risking blockages, which can occur if the diameter is insufficient. In residential settings, this size effectively balances the need for adequate drainage capacity while also minimizing the risk of clogging, making it a common standard in plumbing systems. Additionally, this dimension helps maintain a proper velocity of wastewater flow, which is crucial for preventing sediment buildup within the pipes.