A commercial laundry trench must be resistant to ____ and drain into at least a 4 inch trap.

The correct answer is that a commercial laundry trench must be resistant to alkaline substances because commercial laundry facilities often use cleaning agents, detergents, and alkaline-based solutions in their washing processes. These alkaline chemicals can be highly caustic and can damage materials that are not specifically resistant to such agents.

In addition, the requirement for the trench to drain into at least a 4-inch trap is crucial for effective waste management and to prevent any build-up of contaminants, which could otherwise cause plumbing issues or health hazards.

Resistance to alkaline substances ensures that the trench will maintain its integrity over time, effectively managing the high pH solutions typical in commercial laundry operations, thereby prolonging the life of the fittings and minimizing maintenance requirements.