Which of the problems listed below is commonly found in flushometers?

The common problem found in flushometers that is identified in this question is the failure of the vacuum breaker. A vacuum breaker is a critical component in flushometers that prevents backflow of contaminated water into the potable water supply. When the vacuum breaker fails, it can lead to a variety of issues, including improper flushing and potential cross-contamination. This malfunction can often be identified by a noticeable decrease in the flushometer's performance or issues with water leaking or siphoning.

While the other options identify potential issues related to flushometers, they don't represent the most common problems seen with these specific devices. The missing handle can be a maintenance issue but isn't typically indicative of the unit's operational integrity. A stuck valve can also occur but is less frequent compared to vacuum breaker failures that directly affect water flow and safety. An overflowing tank is more relevant to tank-type toilets rather than flushometer systems, which rely on pressure and direct water flow rather than a tank to function. Thus, focusing on the vacuum breaker highlights a key maintenance concern specifically associated with flushometer operation.