Grease does not dissolve in a drain — it cools and hardens. It goes into the sink warm and liquid, but the pipe in the wall or the floor is at room temperature, often below 20 °C. At that temperature animal fat returns to a solid state and sticks to the pipe wall, where it catches food residue, soap and everything else that passes.
That is why hot water solves nothing. It melts the grease where it is poured in, the grease travels a few metres further, cools and settles there — in a part of the pipe that is harder to reach.
How the deposit grows
The first layer is thin and almost unnoticeable. Its rough surface catches the next layer faster than a smooth pipe would, so the process accelerates itself. In a kitchen working every day a measurable layer forms in two to three months; where there is frying and grilling, faster still.
The first sign is not a blockage but slower drainage towards the end of the shift, when the most warm grease of the day has gone through the drain. In the morning the drain seems normal, because nothing was added overnight.
A grease deposit is not only a flow problem. It is also food for biofilm and a place where drain flies lay their eggs — two things that are hard to explain in a HACCP record.
Why the usual solutions fail
Hot water and detergent. Detergent emulsifies the fat while it is warm. The emulsion separates in the colder pipe and the fat settles out again. The net effect is relocation, not removal.
Caustic soda. It works — the alkali turns fat into water-soluble compounds by saponification. But dissolving alkali in water is exothermic and heats the pipe locally, so in a kitchen where this is repeated every month the PVC joints and rubber seals are the first casualties — more on that here.
Enzyme preparations. They break fats down slowly and need time with no flushing. In a household they work overnight. In a kitchen that runs sixteen hours a day they rarely get the chance.
| Method | Effect | Limitation |
|---|---|---|
| Hot water | Melts fat at the inlet | It settles further down the pipe |
| Detergent | Emulsifies while warm | The emulsion separates in the cold |
| Enzyme preparation | Breaks fat down | Needs hours with no flushing |
| Caustic soda | Saponifies fat, with heating | Damages joints and seals |
| Pressurised water jetting | Strips the deposit mechanically | Requires an outside contractor |
| Mineral granulate | Breaks it down without heating | Prevention, not remedial work on a thick layer |
What helps in a kitchen that runs every day
The sequence that holds up in practice:
- Fat from the pan into the waste container, never into the sink. The cheapest measure there is, and the only one that deals with the source.
- A strainer on every sink — it catches the food residue that gives the deposit something to hold on to.
- A grease trap maintained to a schedule. It deals with whatever reaches it; the pipework between the sink and the trap still has to be maintained separately.
- Mineral granulate at regular intervals, after the last shift. It breaks fresh deposits down before they harden, with no heat and no risk to the joints. The manufacturer's guidance for prevention is one sachet a month; in a heavily loaded kitchen the interval is shorter.
- Pressurised water jetting once a year if the layer is already thick — granulate will not strip it.
If the drain runs but smells
An odour with normal drainage is not grease but biofilm on the pipe walls, or a dried-out trap in a floor drain that is rarely used. Those are different problems and need a different answer — explained in the article on drain smell from a floor drain.