Potential cause / solution to mildew in kitchen drain

braytonakJune 15, 2009

Like many people, I have a problem with a persistent mildew smell from the drains of my kitchen sink. It's not necessarily the disposal as the smell is strong from both sides.

In the last house we lived in we had the same issue, although that house did not have a disposal. I actually changed the pipes in the previous house to try to resolve it. This proved there was mildew in the pipes. Short lived relief. Both houses have one thing in common: the "T" that connects the drain from the sink and the drain from the disposal to the P trap has a small 'flap' that appears to be intended to direct the water from the disposal down to the P trap. This would logically prevent the disposal from causing waste to come flying up the other side of the sink, which is how it always seemed to work when I was a kid.

I suspect that this 'flap' prevents enough airflow that would otherwise allow the drain to breathe and not become a breeding ground for mold.

I never recall my parents having this kind of trouble, which was in homes with both PVC and brass plumbing. Should I find a replacement "T" that doesn't have this 'flap' thing to direct the flow? Would that theoretically allow the drain to breathe enough or am I just reaching for straws?

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That Tee with the little divider that you are describing is properly called a "Baffled Tee" and it is a code requirement.

Baffled Tee's are made in two varieties, a "Vertical Baffled Tee", which is used on the vertical line under the first sink on an "End Waste Kit" or a "Horizontal Baffled Tee", which is installed in the center portion of the horizontal line on a "Center Waste Kit".

Both of the sink drains are open to atmosphere so the baffled tee so air can enter the pipe from either end therefore the baffled tee has absolutely no effect on air flow through the drain lines.

The root cause of your odor problem results from the decaying action of a scum that forms on the inside of the pipes from cooking grease, food particles and soap. The buildup of the scum is even more pronounced when you have a disposal, not to mention that the scum also forms on the inner lining of the grinder cavity in the disposal itself however, there is a very simple and in-expensive remedy.

First off, a disposal should be run a few moments at least once a day. With the water running, when you operate the disposal the water is splashed up inside the disposal body to help keep the offending food particles cleaned out.

About once or twice a week you should run about a handful of ice cubes through the disposal. As the ice cubes grind up they help clean the inside of the disposal body and the cutter wheel. Not only does this help reduce the odor problem, it will actually prolong the life of your disposal.

When you have an odor problem such as you describe you can eliminate it by adding two or three teaspoons of baking soda to the ice cubes.

    Bookmark   June 15, 2009 at 12:06PM
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I second the Ice in the disposal trick. It keeps the disposal clean, sharp and prevents clogs by allowing the disposal to grind the food better.

In the event that the ice clogs the drain, wait a few minutes for it to thaw.

    Bookmark   June 15, 2009 at 1:15PM
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Years ago Insinkerator used to have a note in their owners manual suggesting the use of ice cubes to clean the inside of the disposal cavity.

    Bookmark   June 15, 2009 at 2:22PM
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Thanks, guys! I'll go jump on this. Good thing I have an ice maker to keep up with me. (Otherwise I'd never have ice.)

    Bookmark   June 15, 2009 at 9:51PM
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