The Google has conflicting answers. I come from a background of "everything goes in the garbage disposal", my wife's background is "never put anything in the garbage disposal". I suspect reality is somewhere between us.
Note: I'm talking about the garbage disposal unit under the sink.
I've always put egg shells down the disposal. The "official" word from one manufacturer is:
Most forms of food waste can be put through the food waste disposer — bones from fish and poultry, meat, large meat bones, fish scraps, vegetables, fruit, egg shells, and much more. Very stringy or fibrous foods such as celery should be avoided. Food waste disposers are designed for food waste only and packaging materials should not be put into the disposer.
Given that this manufacturer says you can put large bones in a disposer, I can't imagine that eggshells would do any damage.
And as a practical matter, I've seen name-brand disposers at Home Depot for $100, so even if you felt you were shortening the life of your disposer by a small percentage by putting too much into it, it's not a big deal to get a new one.
If you have a septic tank, avoid using the garbage disposal, especially for anything like egg shells, bones, coffee grounds, and other things that the bacteria in the tank won't eat. Worst case scenario is that they can plug up your leach field for a very expensive repair.
Living in an old house (~100 years) with old plumbing and old pipes, I barely put anything down our drains except liquids. Besides, eggshells are FANTASTIC for your roses and your compost. Why waste them? : )
We live in a major metropolitan area, and I recently replaced our garbage disposer. While it was off I took a look at the pipes under the sink and they were just caked with black rotting gunk inside them. I replaced them with new ones, and since then our cockroach problem seems to have gone away completely. I believe all that rotting crud inside the pipes was a full time food source for the bugs. Used to be if you turned on the kitchen lights at 2am you would see a scurry of activity on the counters. Apparently, now that the food source is gone, they left. Turn on the lights at 2am these days and there are exactly ZERO roaches.
Now we use the disposer for cleaning the scraps off the plates, but that's about it. If there's a large quantity of something that needs to be thrown away, we'll put it in a two Walmart bags and store it in the freezer till trash day.
Most garbage disposals can handle just about anything you put down them, up to and including pieces of bone. The problem is the drain pipe: if you have a long, gently-sloped drain that the material is going through then heavy, granular material (e.g. ground eggshells) will settle to the bottom and accumulate. Dry onion peels can also accumulate, especially when there's grease in the pipe.
I've had both eggshell-based and onion-peel-based clogs in my kitchen drain (which goes 18' across the house without a whole lot of slope). So now I never run either down the disposal.
I had never had a problem with our disposal until today... the day my wife put eggshells in there. There could probably have been other contributing factors.
I have read multiple debates and the controversy is enough to get me to discontinue the practice. Garbage, compost, chickens, or a giant laser, all seem like better options to me!
We give our egg shells back to our chickens. They need the chalk for new eggs and they like it. But I think this isn't really an option for you, unless you sometimes feed the birds in the park or something.
You can eat the egg shell yourself, it's quite healthy (if I can believe the internet).
You can put them in the compost container, but I wouldn't put them in the septic tank. Just throw them away in the garbage.
Biggest no-nos are starches, fats, (Thanksgiving is a plumbers busiest day), proteins, and fibrous vegetables. I live in a city highrise. I do put some egg shells and coffee grinds occasionally. What I do weekly, is put 1/2 cup of baking soda and 1 cup of white vinegar in the drains (disposal and other kitchen drain). Let stand for 1/2 hour or so and follow with very hot water. This is good practice. Also helpful are white vinegar ice cubes. They clean the blades.
I would not put said refuse in a septic system for the same reasons as others gave.
I was always taught the egg shells were good for the pipes, but when our drain clogged, the trap was filled with coffee grounds and egg shells. Perhaps the egg shells would normally be fine, and they only got stuck because of the coffee grounds (which I know should not go down--our guests did not). Even still, after that experience, I now have a policy against egg shells (and coffee grounds) in the disposal.
Many years ago my mom had clogged kitchen pipes; after the plumber cleaned it all out, he advised her not to put egg shells, celery or onion skins down the disposal. I didn't know if the disposals had been vastly improved since then, but sounds like items like these are still questionable.
The key to success in putting anything through the disposal is to avoid putting too much in at one time and don't skimp on running water to flush it down. In that way you can even put eggshells, coffee grounds, and vegetables down your disposal. If you have a lot of leafy or fibrous vegetables to put down, or shrimp shells, you can do it but you end up wasting a lot of time and water; better to just put that much stuff in the trash, or better the compost heap if you have one.
I found on manufacturers site http://www.insinkerator.com/en-us/Household-Products/Garbage-Disposers/Pages/Disposer-Dos-and-Donts.aspx and http://garbagedisposalexpert.com/insinkerator-comparison/ that, for some models, says “Stop worrying about what food you can or can’t put in your disposer”. So, depending on the model
Well since I live in a city with a sewer system I pretty much run everything through my garbage disposal. I replaced the 25 year old original with a new KitchenAid and the guy told me I could run just about whatever I wanted through it. I avoid bones and extremely hard substances but egg shells, peels, left over food, it all goes down and gets turned into paste before being washed down into the city sewer system. So I would say it depends on your disposal and the condition of your pipes. If my pipes were older I would probably be more careful about what I put down the drain.
Growing up my grandma told me that egg shells were good for the garbage disposal. They sharpen the blades. I wouldn't put potato peeling or coffee grounds in it
