Bacon fat, lard, butter, chicken fat, and other greasy substances typically harden quickly. If that happens while the fat is going down your pipes, it coats the drainage system and eventually clogs the plumbing, which can lead to costly repair bills. It’s better to let the fat solidify in a glass jar or leftover soup can, then dispose of it in the regular trash. Avoid dumping cooking fats into a compost pile. They block the oxygen necessary for decomposition and can attract pests.