The Waste Gate
Only a fraction of what goes into the Rock Crusher’s funnel flows out through the thin pipe. To avoid turning the Rock Crusher back into a reservoir of forgotten and zombie rocks, we must discard rocks that are no longer valuable through a waste gate.
The waste gate is a critical Rock Crusher component for implementing a straightforward flow equation: What goes in must come out. The Rock Crusher’s funnel is intentionally larger than the thin pipe; after all, just because a rock is in the backlog does not mean it will be done. But leaving obsolete or forgotten rocks in the backlog plugs up the process and flow, creating friction and waste. Good backlog hygiene demands that we constantly remove clutter from the backlog. Unlike the stack of plates visualization, the Rock Crusher explicitly reveals there are two paths out of the backlog: the thin pipe or the waste gate.