I regularly have heard/read the claim that flushing coffee grounds in the sink can 'clean pipes' and/or 'scrape dirt from the pipes' and so on. (Note this is almost the opposite of the claim this question) Is there any truth in this or is it just an urban myth? I would assume the latter but can't find any sources for this: I can certainly imagine coffee having some abrasive characteristics, but only when applied with pressure, which isn't exactly what happens in the drain pipes?
Quite the opposite, actually.
Avoid putting coffee grounds down the garbage disposal. They won't harm the garbage disposal and they'll actually help eliminate odors. However, they can accumulate in drains and pipes, causing clogs. Best to avoid.
Despite the old wives’ tale that coffee grounds down the sink each day is “good” for the plumbing, we at Atomic Plumbing are here to tell you the truth:
Nothing causes more blockages and clogged pipes than coffee grounds and grease.
Even if you don’t put them down the drain at the same time, they’ll meet up and form a sludgy impenetrable nightmare.
Most household plumbing lines are small, and connect directly to pipes that are only slightly larger. FOG and foreign materials can easily block the sewage flow. A blocked sewer can be a worse problem than just inconvenient and unpleasant. A blocked sewer can cause and overflow that sends pollution to our bayous and Gavelston Bay.
Common enemies to our sewer system
... Coffee grounds and filters
This technique was mentioned in a WCBS-TV report in 2010.
Another great use for coffee grounds is as a drain cleaner. Mixed with hot water, coffee grounds can unclog a drain and help keep it smelling fresh. In the refrigerator it makes a great deodorizer because the grounds can absorb odors.
The article was passed around the web and eventually onto the lifestyle website Lifehacker. The Lifehacker article & comments expanded with a recommendation to use "very hot" water and that the primary benefit was as a de-oderizer.
The risk of clogging drains is overstated, but they should not be used in septic systems. According to disposal maker Insinkerator, coffee grounds don't cause issues with disposals or drains, but can cause problems on unclean plumbing Insinkerator Blog.
Coffee Grounds and Eggshells
There is often the question of using a disposal for eggshells and coffee grounds. In fact, neither of these materials is harmful to a disposal, and will pass through it without a problem. However, problems can arise with household plumbing – especially if it is older, or has not been cleared in some time.
Both coffee grounds and eggshells are sedimentary in nature, if too much is placed in at one time, or if the plumbing is restricted, it can create a clog or a ‘slow drain’ situation. Too help avoid any problems, feed these materials into the disposer gradually, and utilize a strong flow of cold water to help flush it through the pipes.
Several plumbing sites mention that coffee grounds are a form of sediment, & settle to the bottom of septic systems instead of breaking down TheToiletZone.
The EPA lists coffee grounds(along with all other food waste) as things not to put into a septic system How Healthy is Your Septic System
Don’t put food down your sink. Septic systems are not intended to dispose of food waste, coffee grounds, grease, or fat, and, in fact, they will harm the septic tank. Try using a compost pile for non-meat food waste; it will help you avoid paying for unnecessary septic system repairs!
No, it is advised that you DO NOT pour coffee grounds down the drain. According to this article on what not to put down the drain:
This needs to be avoided as there is almost nothing else that will cause your pipes to clog as much as coffee grounds will. When the grounds reach your pipes, they will form a thick sludge that is a plumbing nightmare.