Kitchen grease: where it actually ends up

The pan comes off the stove, the bacon fat is still liquid, and the sink is right there. It goes down with hot water behind it and disappears, which is the whole problem: it disappears from the sink, not from the plumbing. Every kitchen line we open in Lee and Collier County tells the same story, and the story starts a few inches below the drain.

What happens to grease after it leaves the sink

Liquid fat is liquid because it is warm. Within a foot or two of the drain it hits the P-trap under the sink, where water sits at room temperature, and it starts to set. Some of it clings to the trap. The rest moves on as a slurry into the branch line inside the wall, then under the slab, where the pipe is cooler still. There it coats the top and sides of the pipe in a thin film. The next pour adds another film. Coffee grounds, rice, eggshell grit, and the fine particles from the disposal stick to the film and thicken it. A two-inch kitchen line does not clog all at once. It narrows over years until one holiday meal finishes the job.

Further down, in the main line and the public sewer, the same fat meets soap and minerals from hard water and turns into something firmer, closer to a bar of soap than a puddle of oil. Utilities call the large versions fatbergs. They form in city mains under every restaurant district, and a small one forms in the main line of a house where grease goes down the sink every week.

Two myths that keep the line narrowing

• Hot water flushes it through. It moves the grease farther before it sets. The water in your drain line is at ground temperature, and the hot water from the tap is not hot for long once it hits it. All you have done is move the deposit from the trap, where you could reach it, to the line under the slab, where you cannot.
• The disposal takes care of it. A disposal grinds solids. It does nothing to fat, and the fine particles it makes are exactly what a grease film needs to build on. Dish soap does not help either. It emulsifies the fat for a few feet and then lets go of it.

Signs your kitchen line is narrowing

• The sink drains, but slowly, and a plunger helps for a week. That is the pipe closing, not a single clog.
• The disposal side backs up into the other bowl when you run it, because the shared line below the two bowls is tight.
• A gurgle from the sink when the dishwasher drains, since the dishwasher pushes a large volume fast.
• A smell from the kitchen drain that comes back within a day of cleaning the trap. Rancid fat has a smell of its own.
• The line clears and re-clogs. A cable machine punches a hole through a grease plug. The plug is still there, and it closes again.

What to do instead

1. Can it. Keep a coffee can or a jar by the stove. Pour cooled fat into it. When it is full, lid on, into the trash.
2. Wipe the pan. Before it goes in the sink, wipe the pan and the plates with a paper towel. The paper towel goes in the trash.
3. Scrape, do not rinse. Plates get scraped into the trash before they go in the dishwasher. The dishwasher’s drain runs through the same kitchen line.
4. Strain the sink. A basket strainer catches the grit that would otherwise stick to the film.
5. Cold water with the disposal, always, so what fat is on the food stays solid and moves through as a particle rather than a film.

These habits do not clear a line that is already narrowed. They stop it from narrowing further.

What jetting does that a cable cannot

A cable machine is the right tool for a root or a wad of wipes. On grease it drills a hole through the plug and leaves the coating on the pipe wall, which is why a cabled kitchen line comes back within months. A high-velocity water jetter sends a nozzle down the line that scours the full circumference of the pipe wall with water pressure and washes the loosened grease downstream to the main. It is the only method that returns a grease-lined pipe to its original diameter. The plumber runs a camera first, because a jetter is not used on thin cast iron or a cracked section, and again after, to confirm the wall is clean.

Grease is also where the line stops being a DIY problem. Chemical drain cleaners do not dissolve set fat in any useful way, and they damage the cast iron in pre-1975 homes and the chrome trap under an older sink. If the trap is clean and the sink is still slow, the deposit is in the wall or under the slab, and that takes equipment.

Septic systems and grease

If you are on a septic system in Lehigh Acres, Alva, Buckingham, or eastern Estero, grease has a second destination. It floats to the top of the tank as a scum layer, and when that layer thickens past the outlet baffle it moves into the drain field and seals the soil. A drain field clogged with fat does not recover with pumping. Septic households should be stricter than anyone about the coffee can and the paper towel, and should ask the pumping contractor how thick the scum layer is at every service.

If your kitchen sink has been slow for a while, or it has been cabled more than once and keeps coming back, send us a note about what it does and when. A camera down the kitchen line shows whether it is grease, and a jetting is a scheduled visit rather than an emergency.