Oils and fats should not release in the drain. Explain why?

Cooking oil and fats should not be thrown down the drain. They can harden and block the pipes. In an open drain the fats clog the soil pores reducing its effectiveness in filtering water. Also, they may kill microbes that help purify water. Therefor oil and fats should be always discharged after taking due care in the dustbin or if possible, in some suitable dumping place.