Published: 17 October 2026
In short
- Cooking oil and solid fat are the main ingredient of the layer that sticks to the pipe wall as it cools.
- Coffee grounds, tea leaves and eggshells do not dissolve in water and settle at the bottom of the trap.
- Starchy cooking water and dough residue combine with grease to form a sticky blockage.
- Paint, plaster and medicines must be collected separately. The drain is not the place for them.
- A fine-mesh sink strainer catches most of the solid waste on this list before it reaches the drain.
For each item we explain two things briefly: what exactly it does inside the pipe and where it should go instead. You can think of the list as a reminder to stick on the fridge door.
Why do fats come first on the list?
Fats come first because they are the main material of the layer that narrows a kitchen drain. Liquid fats such as frying oil and olive oil flow easily with the water while hot, but when they reach the colder part of the pipe they stick to the wall as a thin film. Butter, margarine, rendered fat and the fat that sets on top of meat broth solidify even faster and thicken this film in a short time.
- 1. Liquid cooking oil: let it cool, collect it in a bottle with a lid, and take it to a used oil collection point when the bottle is full.
- 2. Solid fat and broth fat: let it set in the pot, lift it out with a spoon and put it in the bin. Wipe the pan with a paper towel before washing it.
Starchy water and dough residue
The water from boiling rice, pasta and potatoes leaves a thin starch sludge at the bottom of the pipe. This sludge can wash away on its own, but if there is grease in the pipe it sticks to it and hardens the blockage to a rubbery consistency. Flour paste, crêpe batter or cake batter thickens even more when mixed with water and clings like glue in the bend of the trap.
- 3. Rice and pasta water: keep the sink strainer in place while draining, and pick up the sticky grains left at the bottom of the pot with paper and put them in the bin.
- 4. Dough and flour paste: scrape the bowl and whisk with a spatula first, put the residue in the bin, then wash them.
Three kitchen residues that do not dissolve in water
Coffee grounds, tea leaves from the teapot and eggshells do not melt in water. Because of their weight they settle at the lowest point of the trap, and when they mix with grease there they turn into a sand-like fill. The common belief that eggshells clean the pipe is also wrong. Broken shell pieces simply join this fill.
Tea leaves escape down the drain most often when the morning teapot is emptied in a hurry. A few leaves do not look like a problem, but when it is repeated every day a dark sludge builds up at the bottom of the trap and the sink starts to smell. Turning the teapot upside down over a strainer or a bin bag first easily changes this habit.
- 5. Coffee grounds: empty the cup and the coffee pot into the bin or into a container. Dried grounds can be mixed into potting soil.
- 6. Tea leaves: empty the teapot into the bin or a compost container, not into the sink.
- 7. Eggshells: after cracking the egg, put the shell straight into the bin or a compost container.
Hard, sticky and paper waste
Bone and fish bone fragments lodge crosswise in the trap or the first elbow and act like a dam that holds back everything coming behind them. Fruit and vegetable stickers are small, but because they are plastic and adhesive they do not dissolve and stick to the inner surface of the pipe. Paper towels and napkins do not break up like toilet paper and bunch into clumps as they get wet.
What these three groups have in common is that they never soften with hot water or detergent. Grease at least keeps flowing for a while, whereas a piece of bone or a wad of wet paper stays where it is in the trap no matter how much water you run. If your sink has no strainer, or the holes of the strainer are wide, buying a fine-mesh strainer will catch almost all of this waste.
- 8. Bones, fish bones and hard food scraps: scrape plates into the bin and do not remove the sink strainer.
- 9. Fruit and vegetable stickers: peel them off and bin them before washing, since they slip easily through the holes of the strainer.
- 10. Paper towels and napkins: all of them go in the bin, including the paper you used to wipe off grease. Even a single wet napkin can form a clump in the trap.
Two hazards that reach the kitchen from other parts of the home
After renovation work, brushes and buckets are often washed in the kitchen sink. Paint residue hardens in the pipe and leaves a crust. Plaster and mortar actually set when they combine with water and form one of the hardest blockages to remove. Unused or expired medicines do not block the pipe, but they mix into the wastewater, and using the drain as a way to dispose of medicines is not right.
- 11. Paint, plaster and mortar residue: let the residue in the bucket dry and dispose of it as a solid. Wipe the brush with paper first, then wash it in a separate bucket.
- 12. Medicines: do not pour syrups and tablets down the drain or the toilet. Leave them in the waste medicine box at pharmacies.
What should you do if something has slipped into the sink by accident?
If grease or residue has slipped into the sink by accident, running plenty of hot tap water with a little washing-up liquid straight away largely stops the material from settling in the trap. Do not pour boiling water, because PVC pipe connections can soften at that temperature. If plaster, mortar or a piece of bone has gone down, it is better to take the trap off over a bucket and check inside before turning on the tap, because running water carries these materials to a place you cannot reach.
If the sink has already started to slow down, do not wait for it to fix itself. A kitchen drain that empties late may have several of the items on this list built up together inside it, and every load of washing-up makes that build-up bigger.
