Fats, Oils and Grease (FOG) is the term used to describe materials that when disposed of in the sanitary sewer system, create a hard layer of material that can clog service laterals and main lines. The presence of FOG in the sewer system affects everyone in the community. These materials enter sewer pipes through restaurants and commercial and residential sinks. It can build up and stick to pipe walls, creating problems such as: 

Example of FOG
An extreme case of fats, oils and grease in a sanitary sewer pipe.
  • Clogged pipes causing sewage to flow backwards.
  • Sewage backflows can flow into sewer laterals and up floor drains damaging basements.
  • Sewage backflows can overflow out of manholes, into the street, drain into the storm sewer and eventually reach our lakes and creeks.  Sanitary Sewer Overflows (SSOs) contamination created by FOG can be a Public Health risk if there is direct human contact and can have environmental impacts.  Direct contact with untreated wastewater can cause skin and ear infections and disease. Untreated wastewater can impact the environment with algal blooms, decrease water quality, damaging the habitat of fish, wildlife, and green areas.

Besides preventing environmental and financial problems, measures taken to reduce FOG could decrease Biological Oxygen Demand (BOD) and Total Suspended Solids (TSS) concentrations.

High levels of BOD and TSS in our wastewater are more expensive to treat at the wastewater treatment plant as they require more energy in the treatment process. Ways to reduce your BOD and TSS contributions:

Example of FOG
An extreme case of fats, oils and grease in a sanitary sewer pipe.
  • Minimize the amount of fatty food discharged down drains of kitchen sinks and dishwashers.
  • Maintain grease traps and grease interceptors frequently and properly dispose of waste.
  • External grease interceptors should be pumped, not “skimmed” and properly dispose of waste.
  • Instruct kitchen personnel to dispose of food waste, especially fatty food material, into trash cans as much as possible.
  • Limit the use of garbage disposals in favor of disposing of organic material in trash cans or composting.
  • Use dishwasher and sink strainers to capture solid material.
  • Make sure that plumbing in the food preparation area actually goes to the grease interceptor or grease trap. Make certain that floor drains and sinks do not bypass the traps/interceptors.
  • Make sure that the fryer oil is disposed of in the recycling barrel.

Clean up grease spills with an absorbent material, like cat litter, and dispose of it as dry waste in the trash can.

If you have questions regarding if your facility needs a grease trap, please contact the City of Madison Building Inspection Plumbing Department at 608-266-4346.

Facilities with grease traps/interceptors are required to submit proof of maintenance on an annual basis.  Additional information available on Restaurant Class page.