xtn,
You have already given out to much info. He knows that there is a meter, so city water. If he sees the water pipe at the house, then he has a base line already. There is usually a logical way to run pipe from a meter to a corner of the house. Now if he uses Google map, he can look at the property, using satellite pictures. If he is smart, he will take an eyeball view of the property upon arrival.
If he fails, he can just pass it off as a bad day, illness or a paranormal failure . If he succeeds to accurately map the PVC pipe, then he can have boasting rights , and get his name in the papers, and a You Tube video, and all the other dowsers will add his name to the ones that can, and also sing praises to the wonderment of it all.
You let him off the hook by saying no payback for failure, all he has to do now is take a chance, laugh about it and shrug it off. I am assuming that you have other buried electrical lines maybe other PVC pipe, cable, septic runs, or sewer, etc. Does he get credit for locating other buried stuff?
I wish your place was not to far, I would love to watch the experiment in person.