Never Pour Hot Grease Down the Kitchen Sink

Grease leaves the pan as a liquid and arrives in your pipes as a solid. It coats the walls, catches everything that comes after it, and narrows the pipe until one ordinary evening the sink stops draining. On the municipal scale the same process builds the fatbergs that cities spend fortunes removing.

Nothing you pour after it fixes it. Hot water and detergent only carry the fat further along, to a cooler section of pipe where it solidifies out of reach.

What counts as grease

More than the obvious frying oil: bacon and roasting fat, butter, cream and milk in quantity, mayonnaise and salad dressing, gravy, coconut oil, and the fat that comes off mince. If it is solid or thick at room temperature, or greasy on a plate, it belongs in the bin.

Correct disposal, by amount

• A film in the pan. Let it cool, wipe it out with kitchen paper, bin the paper. Then wash the pan.
• A few spoonfuls. Pour into an old jar or tin kept under the sink for the purpose. When it is full, cap it and bin it.
• A pan of frying oil. Cool completely, funnel back into its original bottle or a sealed container, and bin it — or take it to a recycling point if your area has one. Many councils and some supermarkets collect used cooking oil, and it is worth two minutes to check.
• Bacon fat and dripping worth keeping. Strain into a clean jar and refrigerate; it is excellent for roasting potatoes and keeps for weeks.

Never pour hot oil into a plastic bag or a thin container — it melts through.

Myths that cause blockages

• "Hot water washes it away." It relocates it.
• "Washing-up liquid emulsifies it." Briefly. The emulsion breaks as it cools.
• "The waste disposal handles it." A disposal grinds solids; it does nothing about fat, and grinding food into a greased pipe makes the blockage set harder.
• "Coffee grounds scour the drain." They accumulate and bind with grease into concrete — coffee grounds do not clean the drain.

If the drain is already slow

1. Start mechanical. A cup plunger over the plughole, with the overflow blocked and enough water to cover the cup, clears most early grease blockages — one of the reasons to keep a plunger in every bathroom and one in the kitchen.
2. Clean the trap. The U-bend under the sink unscrews by hand into a bucket. Unpleasant, free, and it is where the blockage usually is.
3. Enzyme or bacterial drain treatment. Slow — overnight or several nights — but it actually digests fat rather than pushing it along, and it is safe for pipes and septic systems.
4. Hot (not boiling) water and washing-up liquid can help a light film in metal pipes. Do not pour boiling water into plastic traps repeatedly.
5. Avoid caustic drain openers as a habit. They generate heat, can damage older pipes and plastics, and make the plumber's job hazardous if they do not work.
6. Call a plumber if several fixtures are slow at once — that means the problem is past your trap and in the main line.

Prevention that takes no effort

• Scrape plates into the bin before they reach the sink.
• Fit a sink strainer and empty it into the bin, not down the drain.
• Wipe greasy pans with paper before washing them.
• Keep the grease jar visible under the sink. A habit only survives if the container is closer than the tap.

Frequent questions

Is it different with a septic tank? Worse. Fat floats in the tank, thickens the scum layer and shortens the interval between costly pump-outs.

Can I compost cooking oil? Small amounts of vegetable oil on paper towel, in a hot compost, at a push. Animal fat attracts vermin and should go in the bin.

What about oil from a deep fryer, repeatedly? Strain and reuse it a few times, then dispose of it properly. Oil that has smoked or gone dark is done: what to do if oil starts smoking.

The sink smells but drains fine. That is usually residue in the trap. Clean the trap, then run an enzyme treatment overnight — the smell is bacteria feeding on the grease that is still there.