Not true as far as I know, but a fun story anyway.

The Superintendant of a high rise office building in a major city had a large, and potentially deadly, problem one winter day.
It would seem that the building sprinkler system was completely off line and, even a small fire could become a giant funeral pyre in just a matter of minuets.
In the building's basement there was a huge, several thousand gallon, water tank that provided all the water nessasary for the sprinkler system. There was also a large pump to dispense the water.
After several hours of attempting to discover the problem and repair the system, the Superintendant called upon a master plummer.
The master plummer arrived a short time later, and the Super quickly ushered the old man to the basement. The plummer looked at the pump, then at the tank. He nodded knowingly, went to his tool box, and took out a small hammer. He walked around the huge tank, tapping in what seemed random locations for about one minuet.
Then, to the surprise and relief of the Superintendant, the pump came back on line and all systems were functional again. Disaster had been averted!
The master plummer then sat down and wrote out a bill and handed it to the Super. "1000 dollars?!" He shouted at the old man, clearly outraged. "All you did was tap on the tank a few times!"
With that, the master Plummer took back the bill, made some corrections, and handed it back to the Super. The bill had been itemized.

It read: Tapping on the tank - $100

Knowing where to tap - $900
--------
Total-$1000
The bill was paid in full.

Hope you enjoyed the story
Kurt