The Answer is:
Excess cooking oil poured down the drain will congeal, stick to the interior of the pipes, and collect over time, obstructing the flow and causing your sink to emanate foul aromas.
Improper oil disposal also causes problems in public drainage systems because it mixes with other trash, such as hair or rags, to form a mass known as a ‘Fatberg.’

If these fatbergs are not removed, they can cause pollution, clog toilets, and block drainage pipes, leading to sewage overflow and flooding in the streets