Comment by presidentender

One of my favorite... solutions, I suppose, was to find a break (not a leak) in a pipe by running current through it and using some sensor (I think the vocabulary is "signal generator," but I do not know). Current does not run further, there is your break; dig and find.

When the pipe is PVC, though, current does not run through it - so what do we do? Why, pump an electrolyte solution, and run your current through that!

It's simple, but it's not done, and so the plumber friend who told me of the original solution patented it, tried to sell it, and found that potential buyers were almost offended at how easy it was. As soon as he'd describe it to people they'd almost think they came up with it themselves. So it is a valuable idea, but it is also utterly worthless.