Thawing frozen drain lines - Fine Homebuilding Tip
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Thawing frozen drain lines

I have a basement that is mostly below grade with a walkout entrance at one end. The door opens onto a sidewalk that is sloped to a drain. As shown in the drawing, the drain is between the basement door and a set of stairs. If the drain is working correctly, I don't have a problem with water backing up and threatening to pour over the door's threshold and into my basement. Problem is, in the winter and the spring, the drain freezes occasionally, allowing water to back up. And no amount of chiseling, heating, prodding and poking would successfully dislodge the ice.

Near the end of our ropes, my son and I finally came upon a foolproof way to clear the drain lines. I've used this method in 3 in. of standing water. Best yet, it can be done with materials typically found around the house or purchased for a few dollars at the hardware store.

First, you need two pipes, one that will fit inside the other. The smaller pipe must fit inside the drain, and the larger pipe must fit around the outer part of the drain. We use the rigid plastic nozzle from our shop vacuum for the smaller pipe. The larger one is a piece of PVC pipe.

As shown in the detail drawing, we use plumber's putty to make a seal around the base of the larger pipe to help hold back the cold water. You can get by without the putty, but it does speed the job.

To thaw the drain, fill a pitcher with hot water and pour it by way of a funnel into the center pipe. The hot water will begin to melt the ice, and the tube will inch its way down the drain. As you continue to pour the hot water down the center pipe, the cooled water will be forced upward into the outer pipe. Keep pouring the hot water until the drain line clears. By the way, our drain has an elbow about 4 in. down, so the pipe can't fall into it. If your drain goes straight down, make sure to hang onto it so that you don't lose it, which would cause a real blockage.

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