PHILADELPHIA (CBS) – How do you dispose of your cooking grease? Local water companies want you to know whatever you do, don’t dump it down the drain.

It’s lurking in the nation’s sewers, and even as close as the sewage line that runs from your house to the main. It’s called FOG — for accumulated fats, oils and grease. In Philly, it’s FROG, since the water department includes tree roots. Where’s it coming from? The Philadelphia Water Department’s Debra McCarty has an answer.

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“Some of it comes from our bodies, but I would say the primary source is people putting oil and grease down the drain, which they really shouldn’t do.”

All that gook builds up in the waste lines like plaque in an artery, until it won’t let anything past. That’s when it gets ugly, as sewage backs up into your house.

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“That tends to be the largest, most frequent problem — it’s between the sewer and the property. And it’s the property owner’s responsibility.”

The best way to prevent the problem says McCarty is to filter and reuse your cooking oil, or put it in a container and out with the trash. That’ll keep your money from going down the drain.

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Reported By Molly Daly, KYW Newsradio