Duct tape is not an approved material for connecting PVC pipe to cast iron pipe. The photo below was from a early 1900's Craftsman style cottage. The waste lines had several leaks in the crawl space.
Attic ventilation rules were developed in the 1940's when attic spaces developed problems with mold and mildew due to excess moisture. With newer construction materials and techniques, houses were being built tighter. The new homes with a tighter envelope, retained more moisture. Some of the normal moisture sources generated include our breath, by cooking, or bathing. As this moisture migrated into the attic spaces, problems began to develop. Proper attic ventilation is designed to move air and moisture out of the attic.