There are a lot of things that can cause a drain to become clogged. It all depends on how they are used and where they are located in the home. Toilets often get clogged because someone has flushed too much toilet paper, a random object or toy, or other toiletries that are not flushable. Even if the toilet itself does not appear to have a blockage, there could be one deeper in the drain. Sink drains tend to get clogged by food, paper or plastic, soap, and even hair. In some cases, tree roots can grow into drains and cause them to become clogged, as well.