The concern is primarily about repeated exposure, large quantities of extremely hot water, unsuitable plumbing materials, or an existing plumbing problem.
Simply avoid making it a regular habit.
What About Older Plumbing?
Extra caution can make sense in older homes, where plumbing materials and connections may differ from modern installations.
If you don’t know what your pipes are made of, there’s little reason to experiment with extreme temperatures.
Normal hot water is generally sufficient for household cleaning.
The Better Kitchen Sink Habit
Instead of relying on boiling water to “clean” your drain, focus on preventing problems in the first place.
Keep food scraps out of the drain, dispose of cooking oil properly, use a sink strainer, and clean the drain periodically.
Prevention is usually easier and cheaper than dealing with a serious blockage.
The Bottom Line
Boiling water isn’t automatically dangerous for every drain, and an occasional pour won’t necessarily damage your plumbing.
But using large amounts of freshly boiling water as a routine drain-cleaning method isn’t always a good idea.
It can potentially stress some plumbing components, and it may simply push melted grease farther down the pipe instead of removing it.
The smartest approach is simple: keep grease and oil out of your drains, use ordinary hot water for normal cleaning, and deal with blockages using the right method.
