Short definition
PVC Schedule 40 (DWV) is the white rigid plastic pipe used for most modern residential drain, waste, and vent piping. It’s lightweight, corrosion-resistant, and joined with a two-step solvent process: a purple primer first, then PVC cement. In Washington, it competes with ABS (black DWV pipe), which is more common in 1970s–1990s housing stock; new work runs about evenly between the two depending on contractor.
What it is
PVC Schedule 40 DWV pipe is polyvinyl chloride manufactured to the dimensional standard for drainage applications under ASTM D2665. “Schedule 40” specifies the wall thickness — the same wall used in pressure piping at lower pressures, but here the pipe is unpressurized and only ever flows by gravity. Joints are made by applying a purple primer (ASTM F656) and a solvent cement (ASTM D2564) that chemically welds the pipe to the fitting. A correct solvent weld becomes monolithic — the joint is as strong as the pipe itself.
PVC dominates new commercial construction and is increasingly common in new WA residential work. ABS still has a strong WA market share, especially in single-family work where contractors learned on it. Both materials are accepted by Washington’s adopted Uniform Plumbing Code.
Why it matters to a homeowner
PVC Schedule 40 is what your DWV repipe will likely use if you’re replacing aging cast iron in a pre-1970 home. The two practical things to know:
- Solvent welds are unforgiving. A “cold weld” — primer skipped, cement applied unevenly, pipe under-inserted into the fitting — develops a slow leak months or years later that’s hard to diagnose. DIY work needs the primer step.
- Mixing ABS and PVC requires the right joining method. Most WA jurisdictions require a banded mechanical coupling (a Fernco or shielded transition coupling) when joining the two; transition cement is not always accepted. If your house is ABS and a repair section is PVC, ask which method your plumber is using.
Common variants / not the same as
- PVC vs. ABS DWV. PVC is white, joined with primer + cement (two-step). ABS is black, one-step (cement only). Both are accepted in WA.
- Schedule 40 vs. Schedule 80 PVC. Schedule 80 has thicker walls — used for noise damping on multi-story stacks or in some pressure applications. More expensive.
- DWV PVC vs. CPVC. DWV is unpressurized and only for drainage. CPVC is for hot- and cold-water supply. Different chemistry, not interchangeable.
- DWV PVC vs. PVC pressure pipe. Same material and Schedule 40 dimension, different ratings — pressure pipe is sized and tested differently.
Common failure modes
- Bad solvent-weld joint — slow leak that develops after install. Diagnosis: cut and replace the joint.
- UV degradation — outdoor PVC unprotected from sunlight yellows and cracks; needs paint or sleeve where exposed.
- Impact crack — basement install hit during framing; usually visible on close inspection.
- Improper transition to ABS — the wrong adhesive or fitting yields a joint that fails over time.