After you’ve whipped up some stir-fry or fried an egg in butter or oil, it may seem silly to scrape away the little bit of oil in the pan into the trash. But oil, butter and other fats used for cooking should never be disposed of down the drain, no matter how small the amount. Over time, melted fat solidifies, collects and gels, clogging your drains and municipal sewer lines. Large pipes get clogged, and sewage can back up and overflow into the streets. So be sure to use a spatula to scrape all the fat into the trash.