can anyone help identify leak?
You apparently have a partial clog in your main drain line.
Since you say that it's (cast) iron, then that means that it is sectional. If it is sectional and that old, then it is probably getting root instrusion into the line at the joints.
If it is roots, a plumber's snake will only punch a hole thorugh them, which will only help for a short while. If you have all of these roots "roto-rootered" out, the roots also will come back every 1.5-2 years after cleaning them out, so that isn't a permanent solution.
The only permanent solution is to replace the underground main drain line with "glued" white plastic PVC or black plastic ABS drain line. The "glued" joints will not allow roots in.
For a temporary 2-year-at-best solution, rent a roto-rooter machine that can handle a 4" drain line, open a cleanout plug, and roto-rooter the line from the house to the street. that should solve all of the problems that you describe until the roots grow back.
Another thing to check for is a partially plugged vent pipe on the roof (leaves, debris, birdnest, etc.). Go up on the roof (carefully) with a garden hose with sprayer. Remove all foreign matter in the vent pipe that you can reach by hand, and then flush the vent pipe down with the garden hose sprayer.
Last edited by Mike Swearingen; 09-10-2007 at 01:36 PM.