I’ve heard multiple times that you should grind ice cubes in your garbage disposal to sharpen the blades. This has always struck me as rather stupid. Today I read that you should sharpen the blades (which are not sharp to begin with, in my experience) with egg shells. Any thoughts?
I’ve always heard that ice cubes clean the blades. Y’know get all the gunk off that just running water can’t hit. And egg shells are supposed to be bad.
My experience with disassembling a disposal to take broken glass out shows that there really aren’t “blades”. What there were were several sets of spinning “teeth” that really weren’t sharp at all. But they would spin, and essentially grind/crush whatever down.
So anything that says it’s supposed to “sharpen” the blades is probably and Old Wives Tale.
I’m sure there are different types of “blades” on different makes. I’m most familiar with InSinkErator brand. Food drops onto a impact plate where it is broken down into small pieces by free-spinning impact lugs. These are just that - lugs. Rather than being chopped or cut the waste is pounded or mangled. From there it spins to the outside of the impact plate where it passes through a set of offset windows where any long bits (think celery) are mangled smaller. The point being there are no ‘blades’ to sharpen.
Sorry if my description was unclear, I have seen them disassembled and was going by memory. I remember being surprised myself that there were no blades.
It’s not to sharpen, but to clean out.
We just shoved about #3 of leftover ice down the disposal last night, and we try to do it a couple times a year. All of the disposals I’ve looked at carefully have nooks and crannies in them. Unlike a nice smooth pipe, these are wonderful spots for food bits, chopped up and flung around by the disposal, to sit and rot. Stuff the disposal full of ice cubes, add water and then turn on the disposal. The ice cubes are chopped up into smaller and smaller chunks, which are flung into those same corners and scour out some of that built up gunk. Add a bit of baking soda to the mix and the disposal comes out smelling much better.
Another place things like ice cubes will clean out is the top of the disposer. Think about the area that you would touch if you had to try and hold the disposer in place by reaching in from the top. I believe ISE reccommends fruit pits for cleaning as well.
And if it helps, try to think of a garbage disposal not as a blender, but rather is a very fast food mill.
I just wanted to add that frozen vinegar works absolute wonders for cleaning a disposal. It’s like ice squared, or even … Um, never mind. 
Both would dull something like a blender blade over time. Disposal blades are nothing like a like blender blade, and there is nothing to really sharpen or dull.
I’d love to know why egg shells are supposed to be bad. I put 2 egg shells down there every single day. They seem to grind up just fine.
I don’t remember ever hearing that, but the only thing I can think of is that the thin lightweight shells might adhere to pipewalls downstream and cause other problems.
The ice theory works for me in terms of cleaning areas that might otherwise suffer from accumulation of rotting bits of organic matter. This (along with lemons and salt) is the same idea behind cleaning coffee pots in restaurants of that latent brown residue that accumulates on the insides of a glass pot.