[jagans]

If the existing run has not frozen, why would the new one at the same depth? Its not like water sits in the line on a waste line, assuming proper slope.

 

[jagans]

No. The Anaerobic bacteria working tirelessly on your behalf create heat which travels back up the waste line and out the vent. I dont think you have anything to worry about, especially if you have never had a problem with your main waste line. You could throw some EXPS (Blue or Pink) over the pipe if you are worried about penetrating surface frost.