For many households, pouring hot or boiling water down the sink feels like a simple, “clean” habit. Some do it to rinse away grease, remove odors, or prevent clogs. Others believe that hot water naturally disinfects drains and keeps pipes clean.
But plumbers and home maintenance experts warn that this common routine can backfire. Pouring very hot water down the sink—especially into certain types of pipes—can create two major problems that most people don’t notice until expensive damage occurs.
So what’s the truth? Is hot water good or bad? The answer depends on your pipes, what’s in your drain, and how you do it.
Why people pour hot water down the drain
Hot water feels like a “quick fix” for kitchen drains because it can temporarily loosen grease and help rinse away small food particles. It can also reduce odors in the short term.
However, experts say this benefit is often short-lived , especially when grease and oils are involved. Grease may melt in hot water, but it can solidify again later as the water cools deeper inside the pipe – leading to bigger blockages over time.
Problem #1: Hot water can damage pipes (especially PVC)
One of the biggest hidden risks is pipe damage , especially in houses with PVC pipes.
Many modern kitchen drains use PVC (plastic) pipe. While PVC is durable, it has temperature limitations. Repeated exposure to near-boiling water can soften the material, weaken the joints, and cause deformation over time. This can lead to:
loose connections
leaks under the sink
rördeformation
cracked seals
reduced pipe life
You may not notice the damage right away, but months later, homeowners often discover leaking cabinets, damp walls, or mold—problems that can become costly repairs.
In older homes, sudden hot water can also stress aging pipes or corroded fittings, especially when combined with expansion and contraction caused by temperature fluctuations.
Problem #2: It can make fat deposits worse
The other big problem is grease buildup – a common cause of blockages in the kitchen counter.
When you pour hot water down the drain after washing greasy pots, the grease can melt and spread further into the pipe system. But when the water cools, the grease can harden along the pipe walls. Over time, it forms a sticky layer that traps:
left-overs
coffee grounds
soap residue
starch (rice, noodles, flour)
This buildup narrows the pipe and eventually causes slow drainage – or a complete blockage.
Even worse, people often repeat the hot water habit more often when the sink is running slowly, inadvertently accelerating the problem.
What you should do instead (safe disposal habits)
Experts recommend safer methods to protect your sink and pipes:
1) Dispose of grease properly
Never pour cooking oil or fat down the sink. Let it cool and throw it away in a container.
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