The most logical place to put things may seem like the drainage system, but this is far from true. When you pour items such as grease down the pipes, not only does it damage your pipes, but it also creates problems for the environment and local wastewater system.
The pipes for the local wastewater can be greatly impacted when large items plug the system up. This includes rags, towels, and diapers. Even small items such as hygiene products and floss can get stuck in the piping and cause issues when the water starts flowing. When hot grease and cold water meet underground, this will start to solidify and greatly clog your pipes.
Years ago, it was recommended to flush medicine down the drain to get rid of it. This is not encouraged anymore, as drains can contaminate the water bodies and have a bad effect on the environment. Wastewater treatment facilities are not made to take these contaminants out of the water.
Be careful what you put down the drain in the future.