Capture and Surface the Waste in Your System

Let's say you're building a system with a few inputs and a lot of outputs. They system is complex. You know that "garbage in garbage out" is true but there are also wastes within the system itself. Say you have two garbage inputs and want to make a good system. So the saying would be "garbage in, gold out". So if some of the garbage is gold, then how do you differentiate the two? You have to squeeze the garbage out and demonstrate the gold. You only know the gold is gold because you know the garbage is the garbage.