What should a plumber fill the vent stack with to pressure test a DWV system?

Filling the vent stack with water to pressure test a drainage, waste, and vent (DWV) system is a standard practice in plumbing. Water is used for this purpose because it is an effective and efficient medium for identifying leaks within the system. When water is introduced into the vent stack, it allows the plumber to see if there are any drop-offs in the water level or if any water escapes, indicating potential leaks.

Water pressure testing also closely simulates the actual conditions a plumbing system faces when in use, as water will be the primary fluid in the system once it is operational. The physical properties of water make it easy to work with and safe compared to alternatives. Additionally, using water allows for easy cleanup and is less hazardous than using substances like oil or glycol, which pose environmental concerns and can complicate the testing process.

In contrast to water, air can be used for testing, but it may not reveal leaks as effectively because small leaks may not produce visible signs or palpable pressure changes. Glycol and oil, while they can be used in specific applications, are not standard practices for pressure testing DWV systems due to their complexities and potential for environmental impacts. Thus, water is the appropriate and widely accepted choice for testing purposes in this