Fats, oils and grease (FOG) go down the drain as liquids, then cool, congeal and stick to the pipe wall, where they react with minerals and trap food particles and wipes. Over months the layer narrows the pipe until it blocks. Prevention means keeping FOG out of drains entirely; removal usually requires hydro jetting rather than a cable.
- Liquid grease does not stay liquid; it cools and hardens a few metres down the line.
- Hot water and dish soap only move grease further down the pipe, where it sets in a harder-to-reach place.
- Garburators add food solids that bind with grease and settle in sags and low-slope sections.
- Hydro jetting is usually the right tool for grease; a cable pokes a hole through it and leaves the rest.
- A container by the stove and a scraper by the sink prevent most household grease problems.
01 /How do fats, oils and grease build up in a sewer line?
Fats, oils and grease enter drains as warm liquids from cooking, dishwashing and food scraps. As they travel away from the sink they cool, and many fats, such as bacon grease, butter and meat drippings, solidify at room temperature or below. Buried sewer pipes in Canada run cool year-round, so grease sets quickly once it leaves the house.
Research by wastewater agencies has shown that grease deposits are not just congealed fat. Free fatty acids from the grease react with calcium and other minerals in wastewater to form hard, soap-like deposits that bond to the pipe wall. That is why old grease in a sewer can be hard enough to resist a cable and why it can build up even when a household only pours small amounts at a time.
Grease usually settles on the bottom and sides of the pipe and collects most heavily at points where flow slows: sags, low-slope sections, joints, and the point where a kitchen branch joins the main line.
02 /Why doesn't hot water and dish soap fix grease?
Hot water and soap keep grease liquid or emulsified only for a short distance. Once the mixture cools in the drain or main line, the grease separates and sticks further down, often in the buried lateral where it is harder and more expensive to reach. The same is true of boiling water poured down a sink to “melt” a grease clog.
Commercial degreasers and enzyme products may help with thin films in small drains, but they do not reliably remove hardened grease deposits from a main line. Caustic drain cleaners can turn grease into soap temporarily and can damage older pipe, traps and the skin and eyes of whoever opens the line next.
Why pour-in products fail on a main line, and what mechanical options a homeowner can reasonably use instead, is covered in can you clear a main sewer line clog yourself?.
03 /What kitchen habits keep grease out of the sewer?
Most household grease problems are solved in the kitchen. These habits cost almost nothing and remove the cause rather than treating the symptom.
| Source | Do this instead |
|---|---|
| Pan drippings, bacon fat, meat grease | Let cool and pour into a sealed container or can; put it in the garbage or your municipality's organics cart if accepted |
| Cooking oil from deep frying | Cool and take large volumes to a depot that accepts cooking oil, if your municipality has one |
| Greasy plates and pans | Wipe with a paper towel before washing; the towel goes in organics or garbage |
| Food scraps | Scrape into the organics cart or compost, not the sink |
| Sauces, gravy, dressings, dairy | Scrape into organics; small residue is fine, pouring leftovers is not |
| Coffee grounds | Organics; grounds bind with grease in the pipe |
Municipal rules on what goes in organics or garbage vary. Confirm locally; in Calgary, check calgary.ca or call 311 for current cart guidance.
04 /Do garburators make grease problems worse?
Garburators, also called food waste disposers, grind food into small particles but do not remove it from the wastewater. Those particles combine with grease and settle wherever flow slows. In a line with a sag, a low slope or root intrusion, garburator use can noticeably shorten the time between cleanings.
Some municipalities discourage garburator use or regulate it for new installations; rules differ, so check with yours. If you use one, run plenty of cold water while it operates and for several seconds after, avoid fibrous and starchy foods such as celery, potato peels and rice, and never put grease through it. The Sewer Maintenance Planner treats daily garburator use as a factor that shortens the recommended cleaning interval.
05 /How do sewer cleaners remove grease from a line?
Hydro jetting is the standard method for grease. A jetter pushes water through a nozzle whose rear-facing jets pull the hose into the pipe and scour the walls on the way out. The force of the water breaks grease off the pipe wall and flushes it downstream to the municipal main. A cable machine, by contrast, can punch a hole through a grease plug and restore flow, but it leaves most of the coating in place, which is why grease blockages cleared by cable often return quickly.
- The technician opens the line if it is fully blocked, often with a cable.
- A camera run shows how much grease is present and where it concentrates.
- The line is jetted with a nozzle suited to grease, working from the cleanout toward the main.
- A second camera pass confirms the pipe wall is clean.
- The technician records findings and recommends an interval.
Jetting pressure and nozzle choice matter, especially on older pipe; sister site SewerJetting.ca explains the equipment in detail. For pricing, see the sewer cleaning cost guide.
06 /How can you tell if grease is your problem?
Grease problems have a recognisable pattern. The kitchen sink is often the first fixture to slow, followed by the main line. Blockages build gradually and tend to recur after cable cleanings. What comes back on the cable is grey or white, waxy, and often smells rancid. On camera, grease appears as a smooth or lumpy coating, usually heaviest along the bottom of the pipe and in low spots.
- Kitchen sink slow while bathrooms drain normally: grease in the kitchen branch.
- Whole house slow, with grease on the cable: grease in the main line.
- Repeated blockages at the same distance: grease collecting at a sag or joint.
- Blockages after holidays or large gatherings: seasonal grease load.
07 /What about multi-unit buildings and restaurants?
In apartment and condo buildings, grease from many kitchens meets in shared stacks and building drains. Kitchen stacks in older buildings often need scheduled cleaning, and one household's habits can affect everyone downstream. The condo sewer cleaning programs guide covers stack cleaning and resident education.
Commercial kitchens handle far more grease and are generally required by municipal bylaws to install and maintain grease interceptors. See restaurant grease interceptors and line cleaning. If grease is already causing trouble in your line, you can request quotes for jetting.
FAQQuestions people ask
Can I pour cooking oil down the drain if I run hot water?
No. Hot water only carries the oil further down the line, where it cools and sticks. Put cooled oil in a sealed container and dispose of it according to your municipality's rules.
Is liquid vegetable oil safe for drains because it stays liquid?
No. Liquid oils still coat pipes, bind with food particles and react with minerals in wastewater to form deposits. They contribute to blockages just as solid fats do.
How often should a grease-prone line be jetted?
It depends on how much grease enters the line. Households that change their habits may not need scheduled jetting at all. Lines with persistent grease, garburator use or a sag may need jetting every one to three years.
Will a cable machine clear a grease clog?
It will usually restore flow, but it leaves most of the grease on the pipe wall, so the line often blocks again. Hydro jetting removes more of the coating.
Do enzyme drain cleaners work on grease?
They may reduce light films in small drains over time, but they are not reliable for hardened grease deposits in a main line and do not replace mechanical cleaning.
Where do I put used cooking oil in Canada?
Small amounts, cooled and absorbed or sealed in a container, typically go in household garbage or organics depending on your municipality. Larger amounts may be accepted at municipal depots. Check your local waste rules.
NETWORKGo deeper across the HAUSE Sewer network
Cleaning grease out of a kitchen drain line
How to clean a grease-clogged kitchen drain line: how fats build up, why snaking alone fails, when to jet, what to do at home, and how to keep the line clear.
SewerJetting.caJetting grease lines: how to actually remove fats, oils and grease
Jetting grease lines explained: why FOG hardens in drains, why snaking a grease clog fails, nozzle and hot water choices, and keeping the line clear.
DrainAugering.caHow to snake a sink drain from the trap arm, not the plughole
How to snake a sink drain: pull the P-trap, feed 1/4-inch cable into the trap arm, get it down the tee, and handle double basins and garbage disposals.