In news Guv Bob typed:
Welp, I'm still poking and digging around the front and not found the
main cleanout yet. Any suggestions or wise cracks would be
appreciated.
. . . ,
There is an "X" mark on the curb 3-ft south of the water meter - this
is where the city dude said the main it likely to be. Straight line
from there to the house is an obvious place, but no cleanout that I
could find.

I usually find the curb vent or sewer cleanout to be near the curb, maybe a
foot or two in from the curb, although I do have one property in
Pennsylvania where it is located in the middle of the front yard. They are
usually at or near the surface, or maybe as much as 4 or 5 inches down if
the grass has grown and built up that area of ground over the years.

The other thing that I do is I look to see if my neighbors have exposed
sewer cleanouts and I look at where they are located in relation to the curb
line. By doing that, I found that one sewer cleanout was on the front lawn
right before the sidewalk (about a foot in) rather than next to the curb --
and I figured that out because that's where the neighbor's cleanout is
located.

When searching, I use something thin like an ice pick or a long thin
screwdriver since I have never found any cleanout or access cover to be more
than a few inches under the ground.

In many towns, if you tell them you are having problems with the sewer line
drainage and that you can't seem to locate the curb vent, they will come out
and find it for you for free.

Curb markings are usually color coded. Green paint means sewer line. Blue
means water. Yellow means natrural gas, etc.

Here's a link with the U.S.A. color codes under "United States":
http://en.wikipedia.org/wiki/Utility_location