What is defined as the lowest portion of the inside top surface of the channel through the trap?

The term being referred to as the lowest portion of the inside top surface of the channel through the trap is known as the P-Trap dip. This part of the P-Trap is crucial because it holds water, which creates a seal that prevents sewer gases from entering the living space. The design allows for the effective trapping of debris while ensuring that regular drainage can occur.

Understanding the function of the P-Trap dip is vital for anyone involved in plumbing, as it plays a significant role in maintaining a sanitary environment by ensuring that odors and harmful gases do not escape from the plumbing system. The water sitting in the dip is what forms the barrier that keeps these gases contained, highlighting the importance of this component in plumbing systems.