Septic tanks rely on to decontaminate the water.
chemicals
microorganisms
the sun
plants

Septic tanks rely on microorganisms to decontaminate the water. These are usually made of concrete and fiberglass with an in-out pipe system. These septic tanks are important in the septic system where sewage is treated naturally by holding its contents long enough for solids and liquids to separate. These things can only be found in areas that lack connection to main sewage pipes that the government had provided. They could be found built in suburbs, small towns, and rural areas and are not suitable for densely built cities. 

You did not show us the image of the burger, but i shall try to answer as best i can.  when purchasing food, always consider the ingredients as well as the person who prepared it. consider if they were hygienic people or not, in case the burger was infected with bacteria. no mortal should place an infected burger into their mouth.