Determining the "biggest" Sch40 PVC pipe can depend on various factors such as length, diameter, and purpose. Sch40 PVC pipes are commonly used for a range of applications including water distribution, drainage, and plumbing. Typically, Sch40 PVC pipes come in standard sizes ranging from 1/2 inch to 24 inches in diameter.

For large-scale projects or industrial applications, custom-made PVC pipes can be manufactured to larger specifications. However, the "biggest" Sch40 PVC pipe would depend on the specific requirements of the project or application. There isn't a single universally recognized "biggest" Sch40 PVC pipe in the world, as it would vary based on the needs of different projects or industries