If it is not the power feed, I vote for the air compressor idea.

I have used toner/tracers for years, and they are SHORT range
even when not in conduit. If you have a friend with Miss
Utility, they will have 38 Khz gear more suited, but....

The air will either announce itself or if it's no-flow, you can
guess the destination is buried and forgotten.

Chisel up enough floor to see the direction is another thought.


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