How to Size Your Own Plumbing Waste Lines

In plumbing, waste lines are known as DWV, or drainage, waste and vent lines. Most waste lines are made out of PVC, a durable injection-molded plastic that resists corrosion and is cheap to manufacture. Waste lines can be sized by determining the ID -- or inside diameter -- and the OD, the outside diameter. Both of these numbers are typically printed on the outside of the pipe. Sizing your pipes is useful during maintenance or repair of your waste lines, as it's important to know the sizes when purchasing fittings and other parts.

Flashlight
Pen and paper

Instructions

- 1
  Locate an area where the waste lines are exposed. Often, this is inside a basement or crawl space.
- 2
  Identify the waste lines by flushing a toilet and feeling each pipe for the rushing water. The pipe that vibrates with water is part of the waste line.
- 3
  Use a flashlight to illuminate the waste line. Look for printing on the side of the pipe. The printing is likely in white or black.
- 4
  Write down the ID number and the OD number. These are expressed in terms of inches. For example, the ID of the waste line may be 1.20 and the OD may be 1.25. Because pipe fittings are sized according to the pipe's OD, that pipe would require fittings that are 1.25 inches.

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