If the oil goes down the drain normally ends up in zones where it could create environmental issues.
First, due to its viscosity, the cooking oil sticks to the insides of pipes and sooner or later it could give origin to undesirable smells or blockages. The oil that achieves to pass through has a high chance of staying for a long time in the sewerage system, producing contamination.
This signifies that it's required a higher amount of work for maintaining the sewerage system in optimal conditions. So it makes the labor more expensive and finally, inherent taxes should be adjusted to it.
Also treatment plants find thanks to oil another problem. A path toward increasing costs and interrelated pollution because this operation of course needs to use chemicals and energy. Breathing odors coming from water treatment plants it's not recommendable because sometimes (although very rare) it could be a source of bacteria.
Finally it's even worse when any kind of oil waste reaches natural zones, as it interacts with the environment in different harmful ways. A known one is when affects to the oxygen exchange in rivers, lakes, ..., causing problems to the underwater life.
Recycling cooking oil, we can help society in general and particularly to different companies that use this resource for numerous purposes like producing detergent, soap, fertilizers, creams, dyes, inks and a long list! Reducing costs, prices and taxes.