Why in some building/plumbing codes, PVC is not allowed for underground building drains? I am not challenging the code, but just trying to understand the rationale..
You are correct, PVC complying to the water pipe standard is not allowed, but PVC comply to the sewer pipe standard is allowed. Neither is allowed above ground, as per usual.
i receive some periodic journal from cast iron manufacturers association and not long ago they submitted some report which shows some results like pvc drainage pipes that release toxins after some years of service, toxins which eventually bypass traps and intoxicate building interiors.
of course, i could not check credentials or find whether some official bodies adopted such report, but it is likely more words will be heard about that.