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Multicast flow (congestion) control establishes a data rate for a multicast session based on prevailing bandwidth availability given other network traffic. This rate is dictated by the sender's path to the slowest receiver. This level of performance, however, may not be in the best interest for the multicast group as a whole. A pruning algorithm is then used to identify and remove some slow members so that the performance is acceptable for the whole group. This paper discusses the conceptual issues with pruning, and proposes practical algorithms for pruning. The crux of the problem is to achieve a balance between speed and accuracy, because increased accuracy tends to require monitoring for a longer time and using more global information. We evaluate and compare different strategies using both simulation and measurement of real implementations.