Search:

If you are in Michigan you can call Arbor East Locating, www.arboreast.com We find private lines only.
The best way is to run a fish tape or sewer cable as far as you can, then tone it with a pipe...

I have to change one too, but if its expensive I will just get another tank.. 1st if its been leaking long the tank may be starting to rust and another problem is just down the road. 2 and take it...