What is required at a hose bibb (sillcock) to prevent backsiphonage?
Not quite. The answer is C: A non-removable hose-bibb vacuum breaker
A hose left submerged in a bucket, pool or sprayer is a backsiphonage path the moment supply pressure drops, so outlets that accept a hose must be protected by a non-removable hose-bibb backflow preventer or vacuum breaker (or an atmospheric vacuum breaker set at least 6 inches above the highest point of use). Water-heater drains, boiler drains and clothes-washer connections are the listed exceptions. "Non-removable" matters because a breaker that unscrews gets removed the first time someone wants a different fitting on the hose.
Reference: UPC 2021 §603.5.7; Table 603.2 (Outlets with hose attachments)
Checked against the official text
Checked against the 2021 UPC text. Washington's exam is written against the 2015 edition, which we have not read for this section, so confirm it against your 2015 book.
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