My wife firmly believes coffee grounds must not be disposed of down the sink drain because they will cause a blockage in the waste pipes. She has it from family and from accounts on the world-wide web.
I am suspicious that this is an urban myth. Ground coffee beans might be no different from any other ground food waste which is disposed of down the sink drain, such as food waste which is ground in the under-sink garbage disposal. As with any food waste, surely they should be rinsed down with water so as not to choke the pipe, but I suspect coffee grounds pose no unique problem.
I know that at my place of employment, we rinse 1–2 cups of coffee grounds down the sink drain at least once daily, have done so five days a week for the eight years I have been employed there, and have not had a blockage caused by coffee grounds during that time. But this is only an anecdote.
Homeowners with septic tanks have to be careful what they can dispose of in the drains, and I have read opinions that coffee grounds can be incompatible with septic tanks, but never accompanied by supporting evidence.
Having performed a Google search for [ coffee grounds plug drain ] I see this is a widely held belief that generates much speculation and many anecdotes, and also that there are widely held counter-beliefs and counter-anecdotes e.g., coffee grounds help scour built-up fats out of the pipes or help eliminate odors (other than coffee odors, presumably). I conclude that factual answers to this question would be widely useful.
