Grease clog

Short definition

A grease clog forms when cooking fats, oils, and grease (collectively, “FOG”) cool inside the drain pipe and stick to the walls. Combined with food residue and soap, the deposit narrows or blocks the kitchen drain over months or years. Boiling water plus dish soap helps fresh grease on metal pipes; mechanical snaking handles the rest.

What it is

Hot grease poured down a drain looks liquid for the first few seconds, then chills as it hits cold pipe walls and solidifies. Each pour adds another thin layer. Soap scum, food fragments, and dairy residue bind into the buildup, eventually narrowing the pipe enough to slow or block flow. Kitchen sinks are the prime location; the same chemistry shows up in restaurant grease traps and apartment-building shared stacks.

Symptoms:

• Kitchen sink slow to drain after dishwasher cycles.
• Gurgling at the disposal or air gap.
• Backup at the dishwasher discharge.
• Standing water that drains overnight.

The fix sequence:

1. Boiling water plus dish soap. Pour slowly down the drain. Works on light fresh grease in metal pipes. Avoid on PVC — boiling water can soften plastic joints (per ug, carter).
2. Plunger (cup-style). Block the dishwasher branch and the sink overflow before plunging.
3. Hand snake or drum auger through the cleanout under the sink.
4. Hydro-jet (pro) for chronic grease in long horizontal runs or shared mainlines.

If the clog returns within weeks, behavior change is the only durable fix: collect grease in a jar and trash it, never the drain.

Why it matters to a homeowner

Recurring kitchen-grease clogs cost $200-$500 each in pro snake calls. The “grease jar” habit costs zero. Cooking-grease disposal also matters at scale — most apartment-building mainline calls trace back to grease, and many cities (including Seattle) bill commercial kitchens for FOG-related sewer maintenance under separate ordinances.

A common myth: liquid grease is “fine” if you run hot water with it. It isn’t. The hot water carries the grease past your trap; it cools and re-deposits a few feet downstream where you can’t see it. Garbage disposals don’t help either — grease bypasses the grinding chamber and re-deposits in the same place.

Common failure modes

• Recurring kitchen-sink slow drain. Behavioral; intercept at the sink with a strainer and a grease jar.
• Grease buildup in long horizontal run before mainline tee. Chronic re-clog without behavior change.
• Apartment-building shared stack. Quarterly hydro-jetting maintenance is common.
• Septic system damage. Grease shortens drain-field life and clogs effluent filters; WA septic owners (over 1 million homes) are especially mindful.
• Dishwasher discharge backup. Grease accumulates at the air gap or branch.

Common variants

• Grease clog (kitchen) vs. hair clog (bathroom). Different fixtures, different remedy.
• Grease vs. soap scum. Heavy overlap; the buildup is usually a hybrid layer.
• Disposal grease pour. No protection — disposers grind food, not fats.
• “Liquid grease is fine” myth. Even hot oil cools downstream and solidifies.

Washington note

WA’s 1+ million septic homes are especially vulnerable to grease damage. Grease lowers the pump-out cadence, clogs effluent filters, and shortens drain-field life — sometimes dropping a 25-year drain field to 10. Septic-home homeowners should keep a strict grease-jar habit and consider an inlet-side grease trap for high-cooking households.

For sewer-connected homes in Seattle and Tacoma, the regional pattern is grease plus paper plus “flushable” wipes accumulating in the mainline over years. Seattle Public Utilities and King County WTD periodically publish FOG-disposal PSAs; the simple rule — let cooking grease cool, then trash it — keeps drains flowing.