I learned here on the SDMB that coffee grounds can’t go in the garbage disposal (that’ll clog yer pipes, buster). I get the sense that chicken skin can’t go in there, either, but I’m no chef. How 'bout these: Chicken bones? Corn husks? Informants?
Google search reveals little, and I think the internet needs a comprehensive list. So here goes:
Coffee grounds: No
Egg shells: ?
I put darn near everything down that damn thing, and can’t remember the last time it got jammed.
That said, I avoid:
Also, I always ALWAYS always run water when it’s on. I think that may be why I don’t get jams, based on a previous thread. I also run it for several seconds after I’m done. Basically the routine is:
Like I said, I never get jams. My father taught me the above routine. He’s the one who had to fix HIS disposal after 5 kids and a wife used it all the time, so he got the procedure down.
There was a recent thread about this and many posters claimed coffee grounds and egg shells were big no-nos, but I’ve always put both down my garbage disposal and never had a problem.
I don’t put stringy things like onion skins and celery through it, but coffee grounds and egg shells? Phfft.
Corn husks would probably jam it, and a lot of chicken skin seems iffy, although I’ve put bits of skin through it, and of course chicken meat and bits of fat down.
I’m just still amazed at the number of posters who think coffee grounds and egg shells will somehow damage it or clog your pipes.
You need to run the water while it’s on, and let it run till the blades are completely cleared.
What’s it for if not to put garage down?
I think it has a lot to do with how much HP the disposal has. I’ve had one of those little 1/3 HP cheapies, and the damn thing would jam and clog all the time. What I’ve had since have been 1/2 to 3/4 HP, and you can grind up nearly anything.
Except the lid off the canned dog food. :o
So cigarette butts are ok?
My brother proved that small snakes will not damage garbage disposals :eek: :mad: :wally: (yeah, I know that one doesn’t work here any more but my brother IS a putz).
Supposedly the guidance is “if you can’t eat it, it can’t go down the garbage disposal” and a plumber once told me I shouldn’t put citrus rinds down. Well, phooey on that, I put orange peels etc. down the disposal all the time and never had a problem. I don’t put bones of any sort (so informants, unless totally boneless vs. merely spineless) would be right out. I think we once had trouble with banana peels, those are evidently best left on the sidewalk 
I wouldn’t try corn husks - I’d think those would be tough enough and stringy enough that they’d be likely to cause damage. When in doubt, toss it in the garbage pail / compost heap.
This bit of advice would apply to eggshells, but IME, they just get pulverized. I can’t see where they’d be a problem.
I put citrus rinds down it, too. Usually the thinner clementine rinds, but they always go away just fine.
Cats
Children
Rocks
Pasta is a bad idea, too. When it hits the blades, it turns into glue, basically. I guess you could feed it down one spoonful at a time with lots of water chasing, but you can’t dump a whole bowl in at once.
I’ve never had any issues with eggshells.
I’ve been told that putting ice down the disposal periodically will help keep the blades sharp. True or false, anyone know? (At least that’s something that definitely won’t clog the pipes…)
I’ve been told not to put celery down the disposal because the strings from it will get wrapped around the blade/shaft. I put small pieces down it and haven’t had a problem.
I always put citrus rinds down the disposal. I have read in several sources that you should periodically put the rinds in the disposal to freshen it. Now I’m wondering, true or false?
Also, I second the recommendation to run the water for a few seconds after shutting it off.
My daughter has illustrated that it is a very bad idea to put the gravel from the fish tank down the disposal. A very bad idea.
I had a problem with my disposal recently. The motor would come on, but the blades wouldn’t turn. I brought it to the attention of the apartment manager and someone was sent out the next day while I was at work. I came home and there was a note on the floor with 2 hacked up pennies on it. Note read: pennies in disposal.
Add pennies to the list.
I’ve never had a problem with eggshells. I will occasionally throw a lemon in there to freshen things up a bit.
Just last summer my 80 year-old mother jammed the pipes by putting a large amount of potato peelings in the disposal. They made it through the blades just fine, but the fibrous mass blocked the drain pipe where it fed into the main waste line.
The plumber suggested that anything with a high fiber content had the potential to do that. He also said that since most washing machines are plumbed to the main kitchen drain lines, it’s a bad idea to do laundry when your kitchen sink is clogged. Thankfully we didn’t learn that lesson the hard way.
Chop the first 2 up into teensy bits
Pulverise the rocks.
No problems at all 
Just to be sure, you’re talking about the drain-mounted grinding units that fit under the sink, right? Here, we call those ‘garburators’ ( a brand name, I believe), and they are quite uncommon.
I believe that many municipalities here ban or restrict them, because en masse they overload the sewage-treatment plants. Not only that, but they are a way to throw away perfectly-good organic material, which then doesn’t enter the city composting system.
So, here at least, the answer to the OP would be, “just about everything”.
Egg shells from breakfast: not a problem.
My wife bakes alot of cookies and twice clogged the disposer and pipes with egg shells. They form some sort of hybrid life form when they clogged up the pipes. The second time, I had to replace a pipe.
The wife now puts them in the trash. Three egg shells won’t clog it. 1-2 dozen and all bets are off.
I read years ago that you should run the water for at least 30 seconds after you turn off the disposal, and if you’ve put anything down that has any type of grease whatsoever, you should run hot water. I’ve not had a clog since. But I also learned the hard way not to throw pasta down in any quantity, and the time my little cactus plant fell in the sink and a bunch of the tiny rocks from the planter went down the disposal was lots of fun, too.
I avoid anything stringy, too; it has a hard time clearing the blade and can jam it up pretty badly. So a lot of things go straight into the trash rather than down the disposal.
If your disposer can’t handle egg shells and coffee grounds, I think you should consider a new disposer.
Do not put corn husks, or artichoke leaves down a disposer. They will form a rope in the pipes. I learned the artichoke one the hard way.
I don’t put large beef bones done the disposer, not because it won’t handle it, but because it take too long to chew them up. I often put chicken bones down it both raw and cooked.
A lemon or lime will make your disposer smell better if you have smell issues.
I’ve personally experienced a egg-shell clogged disposal drain. It wasn’t pretty.
Churches
Witches!
Sorry, couldn’t resist.
Citrus peel may be OK, but a half a lemon seems to defy all grinding efforts.
Pork fat in the disposal isn’t pretty, IME.
This should be obvious, but a month doesn’t go by that some idiot in Cary doesn’t pour a panful of bacon drippings or something down the drain, causing massive sewer problems.
And if you’re going to put broccoli down it, make damn sure it’s thoroughly disposed of and sluiced away, because after 24 hours, half-disposed broccoli leavings in the sink drain start to smell like Satan’s unwiped ass.