Earlydean...I agree with your conclusion (don't mix it), but not with how you got there.
According to Cantex...which makes both types at their Reno plant, using the same amchines and the same dies. here are the differences:
PVC Plumbing pipe is formulated, assuming the pipe will be buried (not exposed to sunlight), and filled with water- which helps support the pipe.
Electrical PVC is rated for exposure to sunlight, and has "stiffeners" added to help keep it from sagging. Thes "stiffeners" would also, I suspect, make the pipe become brittle more quickly, so it probably wouldn't last long as plumbing pipe.
