A memory leak in a Java program occurs when object references that are no longer needed are unnecessarily maintained. Such leaks are difficult to understand because static analyses typically cannot precisely identify these redundant references, and existing dynamic analyses for leak detection track and report fine-grained information about individual objects, producing results that are usually hard to interpret and lack precision. We introduce a novel container-based heap-tracking technique, based on the observation that many memory leaks in Java programs occur due to containers that keep references to unused data entries.