Trap seals are protected when a proper ___________ is established within the trap arm.

The correct answer relates to the importance of maintaining a hydraulic gradient in the trap arm of a plumbing system. A hydraulic gradient is the slope of the water surface in a system, and it is crucial for ensuring that wastewater flows effectively through the plumbing. When a proper hydraulic gradient is established, it enables the water within the trap arm to remain at an appropriate level, which helps protect the trap seal.

The trap seal is the water barrier that prevents sewer gases from entering the interior of a building, and its effectiveness relies on maintaining a sufficient water level in the trap. A proper hydraulic gradient promotes a consistent flow that prevents stagnation and potential siphoning, which could otherwise deplete the trap seal.

In contrast, an air seal is more related to the prevention of pressure differences that might disrupt flow, water level refers to the static position of water, and pressure balance relates to atmospheric pressure affecting drainage, which are not directly responsible for maintaining the conditions necessary for trap seals. Thus, understanding hydraulic gradient is essential in plumbing design and maintenance for effective wastewater management.