One of the more complicated things to clean out from your pipes is grease. When you pour hot grease down the drain, you might think that it will run through the pipes quickly since it is liquid, but this is not the case. Grease that hits cold water coagulates almost immediately, and this can cause some serious clogs. Since grease will repel water, it can stay in place and lead to a stubborn clog.
While hot water sometimes can melt the fat and cause it to move down the pipe, you can’t always rely on this. It might end up just moving the problem further down the pipe.
To prevent clogs from forming in the first place, you should never flush grease down the drain. Instead, use a container where you let it cool down, and after that you can throw it out in your garbage. Some even choose to reuse it for cooking.