The edges of some of my paver bricks are always damp, even though a
ceiling over them prevent rain from ever hitting them. The water meter
doesn't budge when all the faucets are off, so I suspect a leak in the
main waste pipe.

The house is on a slab, and located in central New Jersey, so the pipe
might be a couple of feet below the soil (and below the frost line).

Another winter problem is that the nearby blacktop driveway will raise
about two inches above the concrete garage floor following a couple of
weeks of below freezing temperatures. There had been a gap between the
blacktop and the garage that I just filled, so I don't yet know if
that's how the water was getting below the blacktop. Again, it may have
been leaks from the waste pipe.

Any tips for finding it?

Thanks,

Ray