Used cooking oil must never go down a drain. It cools, hardens and coats the inside of the pipe, and it is the single largest cause of household drain blockages and of the fat deposits that block public sewers. Hot water and detergent do not prevent this, they just move the problem further down the pipe.
Small amounts: cool, solidify, then bin it
For the oil left after a normal pan of cooking, let it cool completely, then either pour it into a sealable container such as an empty jar or the original bottle and put it in household waste, or soak it into kitchen paper and bin that. Chilling the pan in the fridge makes the oil solid and much easier to scrape out. Never pour hot oil into a plastic container or a bin bag.
Larger amounts: take it to a collection point
After deep frying, a turkey fry or a batch cook you may have several litres, which is too much for the bin. Many municipalities run used cooking oil collection, either at a permanent recycling centre or seasonally, and some household hazardous waste sites accept it. Bring it in a sealed container. Used cooking oil has genuine value as a biodiesel feedstock, which is why collection exists at all.
What to do with restaurant quantities
Commercial kitchens do not pay to dispose of used oil, they are collected free by rendering companies who process it into biodiesel and animal feed. Any business generating oil regularly should be on a collection contract rather than treating it as waste.
What never works
| Route | Why not |
|---|
| Kitchen sink or toilet | Solidifies in the pipe, blocks the drain and the sewer |
| Garden or soil | Goes rancid, kills soil life and attracts vermin |
| Compost heap | Attracts rats, and fats do not break down usefully |
| Kerbside recycling | Contaminates paper and card in the load |
| Storm drain | Goes straight to a watercourse untreated |
Reuse it before you dispose of it
Frying oil is not spent after one use. Let it cool, strain it through a fine sieve or muslin to take out the food debris that causes it to break down, and store it somewhere dark and cool in a sealed container. Most oils will take several uses. Discard it when it smells rancid, foams on heating, darkens noticeably or starts smoking well below its usual temperature.
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