Cooking grease is a sewer line problem that starts at the sink

Grease in a sewer line comes almost entirely from kitchen sinks, and EPA says fats, oils and grease poured down drains build up and cause blockages, including in private laterals, where they can lead to basement backups (EPA, Appendix L). The fix is mostly a habit: keep it out of the drain in the first place.

Warm grease runs freely when it goes down the sink. It cools in the pipe, sticks to the walls and catches food scraps, wipes and anything else passing by. In an older house the building drain may be cast iron with a rough interior or clay with offset joints, and both give grease something to grip. The buildup narrows the pipe a little at a time until a slug of debris stops the flow.

What EPA says to do

EPA's guidance on fats, oils and grease, often shortened to FOG, is short:

• Collect grease in a container and put it in the trash.
• Scrape plates and pans into the trash before washing.
• Do not pour FOG down sinks or toilets.
• Do not put greasy food waste down the garbage disposal.

FEMA's homeowner flooding guide gives the same advice and adds that meat and bones should not go through the disposal (FEMA). The New York State Department of Environmental Conservation suggests sink strainers and keeping grease, hair and coffee grounds out of drains, and recommends a plunger or snake rather than chemicals when a drain does slow down (NYS DEC). On chemicals, see drain cleaner safety.

The scale of the problem

In its 2004 report to Congress, EPA said it believed FOG contributed to approximately one out of every five sanitary sewer overflows nationally. That figure is more than 20 years old, but it shows why sewer agencies focus on kitchen habits. EPA's current overflow guidance still lists FOG among the main materials that create blockages (EPA SSO FAQ).

The same 2004 report says enzyme additives can be used to break up scum, grease and other accumulated organic matter and to control odors. That describes how collection systems use them; it is not a substitute for keeping grease out.

What local codes require

Two southern Westchester municipalities write grease into law. Under the lateral chapters of their codes, owners in Rye (city) and in Mamaroneck (village) must keep the pipe clear of roots, grease and solids (Village of Mamaroneck Code ch. 282; City of Rye). Both also require a lateral inspection before a property changes hands; see selling a house and the sewer lateral certificate. For other towns, ask the building department.

Because the lateral is generally the property owner's responsibility in Westchester County, a grease blockage between the house and the main is usually a private repair (Westchester County DEF).

Signs it is grease

Kitchen drains that slow first, then recover, then slow again are a typical pattern. When the blockage moves farther out, into the shared building drain or lateral, other fixtures start to show it. See signs of a sewer line problem and main sewer line clog for what to do next. Clearing a grease-packed lateral is plumber work, usually by cable or jetting; see hydro jetting vs a cable machine.

Key facts

• EPA says FOG can block private laterals as well as municipal sewers, resulting in basement backups (EPA).
• EPA's advice: collect grease in a container for the trash and scrape plates before washing (EPA).
• In 2004, EPA said FOG contributed to about one in five sanitary sewer overflows (EPA).
• FEMA says not to pour grease down drains or grind meat and bones in the disposal (FEMA).
• Lateral codes in Rye (city) and Mamaroneck (village) bar roots, grease and solids from private laterals (Village of Mamaroneck Code).

Sources

• US EPA — Report to Congress, Appendix L
• US EPA — Sanitary Sewer Overflow Frequent Questions
• FEMA — Urban Flooding: Guidance for Homeowners and Renters
• NYS DEC — Household Hazardous Waste
• Village of Mamaroneck Code — Chapter 282, Sewers