Trap arm distance from trap outlet to vent connection: maximum 3.5 feet; exceeding this breaks trap seal and releases sewer gas.
Horizontal DWV pipe support: every 4 feet; vertical stacks: every 10 feet with additional supports immediately above and below fittings.
Use 45-degree elbows for smooth flow; prohibited: 90-degree elbows for horizontal-to-vertical transitions; use two 45s or long-radius fitting instead.
Sanitary tees required for proper drainage pattern: center inlet, side outlet; wyes allowed for angled branch connections.
Fixture units: toilet 4, shower 2, bathtub 2, lavatory 1, kitchen sink 2; branch sizing depends on load and slope.
Fire-stopping required at all floor and wall penetrations; use fire-caulk or firestop putty to prevent fire and smoke spread.
Mechanical protection: rigid sleeves or boxing required for PVC/copper pipes in areas subject to physical damage (basements, crawl spaces).
Individual vent: dedicated to one fixture (most reliable); common vent: shared by two fixtures (low to high only); wet vent: carries drainage plus venting (strict fixture rules).
Vertical stacks require continuous support or support every 10 feet; horizontal runs must not sag; all pipes secured at direction changes.
Drain: Carries water and waste away from fixtures.
Waste: Collects multiple drains into larger lines.
Vent: Lets air in to maintain trap seals and keep water moving.
Every fixture needs a trap (blocks sewer gas), a drain (minimum size for that fixture), access to venting (direct or through other vents), and support and protection during rough-in.
I've been doing this for 30 years, and I'll tell you: get DWV wrong and the inspection fails. Get it right and you're solid.