1. HDPE pipe - 4"

    I have some 4" HDPE pipe on hand and wanted to know the correct size to use. I see many different ID (inside diameter) sizes online. The HDPE I have is for pressure pipe (water mains) and the walls of the pipe are thick. The inside diameter is very close to 3.9. Would a 4" shell still fit? Does anyone else use HDPE water main pipe or just purchase from a known vendor that sells HDPE mortars?