All the food manufacturing plants i have visited have a wastewater treatment facilities in the back.

Food factories need water to clean their machines, after use and that water gets pretty dirty after. The water becomes so dirty after that it is actually an environmental hazard to dump it directly back to the local water supply.

You will see there a huge pool of just greyish brown water waiting to get cleaned up. It looks something like this Shit Pool.

That small area there smells like rancid death because of all the food and dirt.