Fatty dishes like roast goose, duck breast or fondue tend to leave cooks wondering about the same thing: What do I do with the leftover liquid fat? Try not to follow your first impulse if it’s to pour it down the sink or into the toilet. Doing so can do serious harm to your pipes and the sewage system at large, waste water officials in several countries have been warning citizens. The problem is that temperatures in the sewage system are relatively low, meaning the fat swiftly goes hard, causing blockages in pipes in your home. Incorrectly disposed of grease also causes problems in the public …