Hi m

Don't waste your time!

More often than not there is no continuity in cast iron waste piping.
Joints are packed with Oakum and then lead poured in the bell to seal
out sewer gasses. The Oakum acts as an insulator and the lead is not
much better than a cold solder joint, electrically speaking.

If a vent stack did have a good ground and ever did take a good
lightning hit there would be lead flying all over the place.
You rarely hear of a vent stack being hit BECAUSE it is a very poor
ground, if grounded at all.

TTUL
Gary