Final answer:
Access to air-admittance valves should be 'accessible', as these mechanical devices are crucial for allowing air into plumbing drainage systems while preventing sewer gas escape. They must be accessible for maintenance and code compliance.
Step-by-step explanation:
Access should be provided to accessible air-admittance valves. Air-admittance valves are mechanical devices that allow the flow of air into a plumbing drainage system without the escape of sewer gases into the building. They are a critical component of modern waste systems, used to preserve the water seal in traps without needing to vent through the roof.
The accessibility of these valves is important for maintenance, testing, and replacement purposes. In many building codes, there is a requirement that air-admittance valves be installed in locations where they can be accessed, such as in an attic, crawl space, or under a sink with an access panel.