Why You Should Never Pour Cooking Oil Down the Drain

What actually happens to the oil

Oil poured down a warm drain looks like it’s disappearing, and for the first metre or two of pipe, it is. But pipes get cooler further from the sink, and oil starts to solidify as soon as it drops below body temperature. It doesn’t flow away, it coats the inside of the pipe and slowly builds up layer by layer, the same way arteries narrow over time.

Why it’s worse than most blockages

A blockage from hair or food scraps is usually a single clump in one spot. An oil blockage is different, it’s a coating that narrows the entire pipe over weeks or months, so by the time you notice slow drainage, there’s often a significant buildup that basic plunging won’t clear. It usually needs proper jetting to strip the pipe walls back to clear.

It’s not just your problem either

Poured oil doesn’t stop at your boundary wall. It travels into the municipal sewer line, where it combines with oil from every other household doing the same thing, forming what’s known internationally as a ‘fatberg’, a solid mass that can block entire street sections of sewer line.

What to do instead

• Let the oil cool completely in the pan before dealing with it
• Pour it into an old tin, jar, or the original container and let it solidify
• Bin it once it’s solid, or take larger quantities to a recycling depot that accepts used cooking oil
• Wipe greasy pans with a paper towel before washing, rather than washing the grease straight down the drain
• For small amounts of grease on dishes, a squeeze of dish soap and hot water helps break it up before it reaches the pipe

If it’s already blocked

If your kitchen sink is already draining slowly or not at all, don’t keep pouring hot water and hoping, it often pushes the problem further down the line rather than clearing it. A proper assessment tells you whether rodding will clear it or whether jetting is needed to fully strip the pipe.

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