In rec.gardens Mike wrote:
Last fall, I planted a Japanese Tree Lilac in my front lawn...it is
currently 7 feet high and is supposed to get between 15-25 feet. However
being a total newbie, I didn't consider where my sewer line is and I think I
may have planted the tree nearly on top of it.

From experience in an older house, you may have root problems in your
sewer line. We have to flush copper sulfate once a month and have our
sewer line roto-rootered once a year from roots from a tree that was taken
out years ago.

What I recommend before planting large things like trees is to call your
local utilities and have them mark the lines. I'm very glad we did or we
would have planted a tree right over our gas line.

As for being over your sewer line, even beyond getting roots in it,
imagine if you need to have work done i the future - you will need to dig
up the tree! I would recommend moving it now, and call to have your lines
marked before you plant!

Meagan