Hiya Lynn, Welcome to the latter 20th century.
 
We have at least two drainage "pipes" at Curles. One of these (filled
in the 1810s, probably in use throughout the 18th c) may have had
some kind of wood lining. It drained the kitchen cistern and ran to a
"stewpond" at the bottom of the terrace. From there I believe it
watered the gardens, but I need to do more excavation in the garden
area to be sure of that. The second was about 100' away, ran in the
same direction to the stewpond, etc., but we have found fragments of
hand-made terra-cotta pipe in it. It drained the laundry, and I
believe it is a later (late 18th c) feature. We haven't excavated it
yet. On wooden pipes, you should talk to Dennis Pogue and/or Essy
White. I'm think they had evidence--documentary or archaeological--
for wood being used in one or two of the drains at Mt. Vernon.
Finally, there is good documentary evidence for wooden pipes being
used in the public water system in Richmond in the early 19th c.
 
Hope some of that's useful.
 
Dan Mouer