Grease
When you pour grease down the drain it sticks to the inside of your pipes and the pipes in the street. This can cause the entire pipe to become clogged over time. Other oil-based products are also dangerous to pour down your drains, such as cooking oil, salad dressings, butter, mayonnaise, and fat. If needed, make sure to let the grease cool first, then dispose of it in the trash instead.
Flour
Flour coagulates when mixed with water. This can clog your pipes by coating the edges and catching other bits of disposables trying to make their way down. Always throw your flour, whether mixed with water or not, in the garbage.
Medication
If you flush your unused or expired medication or crush it up and pour it down the drain, those chemicals will be leaked back into your drinking water and the environment. Always make sure to dispose of unwanted medication at your local pharmacy or police department, which will have access to medical waste disposal units.
Produce stickers
Many times people wash their fruit and forget to take the sticker off; it falls in the sink and you eventually just let it go down the drain. Peel them off before you wash your fruit and dispose of it properly. Those little stickers don’t dissolve in water and can clog your pipes and block screens and filters or pumps at the water treatment plant.
Credits: rd.com