Vent Stack - Clogged

You need a ladder, a flashlight, and a strong stomach. After locating the vent pipe (a small, gray or black PVC or cast-iron stub poking out of the shingles), you shine the light down into the abyss. If you see daylight, you’re fine. If you see darkness, or a mat of squirrel nest, you’ve found the culprit.

The Silent Gurgle: Why a Clogged Vent Stack Turns Your Home Upside Down vent stack clogged

The fix is not in the basement. It is on the roof. You need a ladder, a flashlight, and a strong stomach