How do I find intermittent leaks and hidden plumbing problems?

You can diagnose most issues now, but the intermittent ones and the buried ones still beat you, and that's the honest edge of this trade. A leak that only shows sometimes, a problem hidden behind a wall, these defy the straightforward methods that work everywhere else. Getting stumped by them doesn't undo everything you know. The hard cases yield to patience, not force. An intermittent leak has a pattern, it happens under certain pressure, certain use, certain temperature, and finding that pattern is the whole game. Buried problems reward the person who reasons from what they can see to what they can't, ruling things out one by one instead of guessing. The skill you're growing is systematic elimination, and it's slower and quieter than the flashy fixes. Next time one baffles you, resist the urge to open everything up at once. Write down what you know, what conditions make it appear, and test one theory at a time. Let the problem reveal itself through the pattern. The tough cases aren't beaten by knowing more. They're beaten by refusing to guess and following the evidence wherever it goes.