Can I Pour Cooking Oil Down the Sink If I Run Hot Water After?
Cooking oil, still hot and liquid right after use, seems like it should pour down the sink drain without issue when followed by a bit of hot water. The reasoning seems sound, but it ignores what happens further down the pipes.
Why hot water doesn't solve the problem
Hot water does keep the oil liquid while it passes through the immediate drain, but it gradually cools as it moves away from the pour point, all along the path through the plumbing. The oil then turns solid or semi-solid further down the system, right where it's hardest to reach and remove.
What happens over time
| Stage | What occurs |
|---|---|
| First few pours | Oil seems to drain away with no apparent problem |
| Gradual buildup | Cooled oil sticks to the pipes' inner walls |
| Passage narrowing | Other debris (food, soap) sticks to the accumulated oil |
| Complete blockage | Drain fully clogged, often at the worst possible time |
Why it's especially problematic in winter
In Quebec, part of the plumbing system running toward the outside or an unheated basement can be exposed to colder temperatures, speeding up the oil's solidification well before it reaches the main sewer line.
What to do with used cooking oil
Pouring the cooled oil into a sealed container (like its original container or a can) and disposing of it in the trash or at a specialized collection point, available in several Quebec municipalities, avoids the problem entirely. Wiping pans and pots with a paper towel before washing also removes a good portion of the grease residue before it reaches the drain.
If the drain is already clogged from accumulated oil
Professional drain clearing is generally needed to fully remove hardened oil buildup in the pipes — standard chemical drain cleaners are often ineffective against this type of extensive greasy blockage.
Frequently asked questions
Does dish soap help dissolve oil in the drain?+
It helps disperse the oil a bit, but doesn't eliminate it from the pipes — the oil still ends up settling further down the system.
Do all oils cause the same problem?+
Yes, including vegetable oils, melted butter, and animal cooking fat — all eventually solidify as they cool in the pipes.
Can a chemical drain cleaner fix an oil blockage?+
Rarely effectively for a significant buildup — these products are mainly designed for other types of organic blockages.
Where can I dispose of used cooking oil in Quebec?+
Several municipal ecocentres accept used cooking oil in a sealed container — check the services offered by your municipality.
Get a free quote
More to know before your project.
By Julien Fortin — RBQ-licensed plumber, 10 years of experience in residential plumbing
Updated on July 22, 2026