Dear Tech Abby: Do I have to use a crushed stone backfill for my PVC sewer pipe installation?That 70's EngineerDear That 70's Engineer: Good question. the answer is "maybe".. Well, let me expand on that. First, when talking about PVC sewer pipe, remember that PVC products are commonly used in both gravity flow sanitary and storm sewer appliions (typically 4" – 36 ...