Drain Clogged With Grease: How to Break It Up

Grease goes down the drain as a warm liquid and sticks to the pipe as a cold, waxy paste. That is why a drain clogged with grease usually builds slowly over weeks and then seems to stop all at once. The fastest home fix is to soften the fat with very hot water and a strong grease-cutting dish soap, then physically break up what remains with a plunger or a drain snake. For recurring buildup, a monthly enzyme treatment keeps the pipe walls cleaner without the risks of harsh caustic chemicals.

What does not work well is simply pouring boiling water and walking away. Heat melts the grease temporarily, but it cools and re-solidifies a few feet farther down the line, often in a spot that is harder to reach. The goal is to move the fat all the way into the main drain or scrape it off the pipe walls, not just relocate it.

Below is a step-by-step plan that starts gentle and escalates only when needed, with tools, troubleshooting, typical costs and clear signs it is time to call a plumber.

Why a Drain Clogged With Grease Keeps Coming Back

Fats, oils and grease, often abbreviated FOG, are the most stubborn kitchen clog because they do not just block the pipe, they coat it. Bacon fat, butter, cooking oil, salad dressing and even the residue from rinsing greasy pans leave a thin film on the inside of the drain. Food particles, coffee grounds and soap scum stick to that film, and the layer thickens until water can only trickle through.

The coating also reacts with minerals in your water to form a harder, soap-like deposit. That hardened material is why a grease-clogged sink can resist plungers and hot water alike. Horizontal runs, trap arms and places where the pipe runs through a cold exterior wall or unheated crawlspace tend to collect the most, because the grease cools fastest there.

Garbage disposals do not solve the problem. They grind food into smaller pieces, but ground food mixed with grease actually makes a denser sludge in the line.

Tools and Supplies You Will Need

• A kettle or large pot for heating water
• Grease-cutting liquid dish soap
• A cup plunger (flat-bottom, meant for sinks)
• A hand-crank drain snake, 15 to 25 feet, with a 1/4-inch cable
• An enzyme or bacterial drain cleaner for maintenance
• Bucket, rubber gloves, safety glasses and old towels
• Channel-lock pliers for removing a P-trap
• Baking soda and white vinegar (optional, for mild buildup)

If you have a double sink, grab a wet rag or a stopper to seal the second drain while you plunge. Otherwise the pressure escapes through the other side instead of pushing on the clog.

Step-by-Step: How to Clear a Grease-Clogged Sink

1. Remove Standing Water

Bail standing water into a bucket so you can work with the drain opening exposed. If the sink has a garbage disposal, switch it off and unplug it or turn off its switch before reaching near it.

2. Hot Water and Dish Soap

Squeeze a generous amount of grease-cutting dish soap, roughly a quarter cup, directly into the drain. Follow it with a pot of very hot water from the kettle, poured slowly in stages. Let it sit for 10 to 15 minutes, then repeat. The soap emulsifies the fat so it can move with the water instead of re-sticking to the pipe.

One caution: if your drain lines are PVC, use water that is hot from the kettle but not at a full rolling boil. Very high temperatures can soften plastic fittings and loosen joints, especially on older installations. Porcelain sinks can also crack from a sudden temperature shock, so pour into the drain opening rather than across a cold basin.

3. Plunge While the Grease Is Warm

Right after a hot water flush, fill the sink with 2 or 3 inches of warm water so the plunger cup is submerged. Seal the second drain on a double sink, and if you have a dishwasher, clamp its drain hose so the pressure does not blow back into it. Plunge with 15 to 20 firm strokes, keeping the seal tight, then pull away sharply. Softened grease moves much more easily than cold grease.

4. Clean the P-Trap

If water still drains slowly, place a bucket under the sink and loosen the slip nuts on the P-trap by hand or with pliers. Remove the trap and scrape out any grease, then check the trap arm going into the wall. It is common to find a thick layer of fat right where the arm enters the wall. Reassemble the trap, hand-tightening the slip nuts and then snugging them a little more with pliers.

5. Snake the Line

With the trap removed, feed the drain snake cable directly into the wall pipe. Crank the handle clockwise while pushing gently. When you feel resistance, keep rotating and work the cable back and forth; the tip will bore through and scrape the grease. Pull the cable back periodically and wipe off the gunk. Once you break through, reinstall the trap and flush with hot, soapy water for several minutes to carry the loosened grease into the main line.

6. Follow Up With an Enzyme Treatment

After the line is flowing, pour in an enzyme or bacterial drain cleaner at night, when the drain will sit unused for several hours. These products digest remaining fats over time and help keep a grease-clogged pipe from re-forming.

Enzyme vs. Caustic Drain Cleaners for Grease

Store shelves are full of chemical drain openers, and it is worth understanding the difference before you buy one.

Caustic cleaners can work on grease because lye turns fats into soap. However, they generate heat, can splash and burn skin and eyes, and may harm older metal pipes or plastic fittings with repeated use. Never mix different chemical cleaners, and never plunge or snake a drain right after pouring a caustic product in, since it can splash back. If you have already used one without success, tell your plumber before they start work.

Baking soda and vinegar create an impressive fizz but are relatively weak against a heavy grease clog. They are fine as a mild freshener for a slow drain, followed by hot water.

Troubleshooting Grease Clogs

• Drain clears, then slows again within days: Grease has moved farther down the line and re-solidified. Snake deeper, then follow with enzyme treatments.
• Both sides of a double sink are clogged: The blockage is past where the two drains meet, likely in the trap arm or wall pipe. Snake from the trap arm.
• Dishwasher backs up into the sink: This is a classic grease clog sign, since both share the same drain. Clear the sink line and check the dishwasher’s air gap or high loop.
• Snake hits a hard stop: You may be hitting a fitting or elbow. Try a slower, firmer rotation, but stop if the cable kinks.
• Gurgling or slow drains elsewhere in the house: The clog may be in a shared branch or main line, which calls for professional equipment.

How to Prevent Grease Buildup in Your Pipes

Prevention is far easier than removal. Pour cooled cooking fat into an old can or jar and throw it in the trash. Wipe greasy pans with a paper towel before washing them. Use a sink strainer to catch food scraps, and scrape plates into the trash or compost rather than the disposal.

Running hot water after doing dishes helps a little, but it is not a substitute for keeping grease out. A monthly enzyme treatment is a good habit for kitchens that cook with a lot of oil.

Typical Costs to Clear a Grease-Clogged Pipe

DIY supplies are inexpensive. A cup plunger and a hand snake usually cost in the range of a modest hardware-store purchase, and enzyme cleaners are a small recurring cost. For a plumber, a standard kitchen drain cleaning typically runs in the low to mid hundreds of dollars, depending on location and access. Hydro-jetting, which uses high-pressure water to scour grease from the pipe walls, costs more but is often the most thorough solution for heavy, recurring buildup.

When to Call a Plumber

Call a licensed plumber if multiple drains in the house are slow or backing up, if water comes up in a floor drain or tub when you run the kitchen sink, or if you smell sewage. Those signs point to a main line or sewer problem, which is beyond household tools and may involve code-regulated work. A plumber can run a camera through the line to locate the clog and use motorized augers or hydro-jetting to remove grease buildup completely. Also call if you have already used a caustic chemical that did not work, so the plumber can take proper precautions.