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Clogged Sink Drain in Cold Weather

Northern winter temperatures effect drainage, as well as water piping.

You are washing dishes and pull the plug to allow the water in the sink to drain. Suddenly, the drain stops. You try drain opening chemicals. You plunge the sink. You attempt to use a drain auger (cable or snake). Nothing is working.

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As you attempt to restore flow to the drain, you will notice one of two conditions. You cable so far, and your cable seems to have hit a brick wall. Or, you cable until you have no cable left and have not encountered any resistance and still no drainage. Aside from having grease buildup or food blocking the drain line, frozen drain piping may be the reason your sink will not drain. In the illustration above, freezing occurs two ways.

If your sink is on  an outside wall, as water is run through the drain, over time, layers of ice build with every use of the sink.  Water runs in and settles at a point where the temperature inside the wall is freezing or below.  Each time the water is run, another layer of ice builds on top of what was previously formed.

If you have a garbage disposer (garbage disposal), you will actually accelerate the process of creating a blockage.  What you are doing when using your disposal during freezing conditions is not just adding water to the drain as it is building the restricting layers of ice.  But, you are adding density. Build up occurs faster.  So, in freezing weather, avoid using the garbage disposer.

In addition to the description above, another way for blockage to occur is by restricting air flow.

Vapor from sewer gas or steam from hot water rises and settles against the interior of the vent pipe.  Given enough time, the vent becomes restricted with a buildup of frost, formed by vapors and or steam.

How to thaw your frozen drain.  First, be sure the vent is not the problem.  If you are cabling your sink drain and encounter no resistance, know your vent is within 6 ft. – 8 ft. from the trap and you have put 10 ft. to 15 ft. of cable in the drain line, you may have restriction in the vent.  Go up on the roof and look down the pipe that is smallest and comes through the roof, closest to your sink location.   If you see frost, in the pipe, run water from the garden hose down the vent.  If the vent overflows, push the hose down the vent pipe as far as it will go.  Chances are, you are now getting the warmer water directly onto the spot where the vent pipe is restricted with frost.  When the water begins to drain, congratulations, you have now restored the vent and may now have a functional sink drain, providing you do not also have a frozen drain in the wall.

If your drain arm in the wall has frozen, allow heat to the cabinet where the pipe disappears into the wall.  Now, you are going to have to go through a long process of running scalding hot water until the sink backs up, vacuum the water completely out of the sink and the drain line.  Repeat the process.  Eventually, the ice will melt and you will have to minimize the use of that sink until the weather returns to normally expected temperature.  I did this recently and it took over two hours to restore flow to the drain.