Eggshells in the garbage disposal is a topic of debate among plumbing experts. The shells do not actually sharpen the blades. Instead, the matter centers around whether the shells keep the grinders and plumbing system clean.
What Proponents Say
Eggshells are coarse and mildly abrasive. As a result, some plumbers advocate tossing a few down the disposal and grinding them. They say the rough texture of the shells helps clean the grinding mechanisms inside the disposal. While the shells are not tough enough to actually hone the steel grinders, removing food buildup helps the grinders tear through food waste more efficiently.
What Opponents Say
Other plumbers take a different point of view, expressing two fatal flaws attached to tossing eggshells down the disposal. The first is the membrane on the inside of the shell. Plumbers in the "do not recommend" camp say the membrane sticks to grinders, lessening how well they cut food waste, especially over time. The other problem they see is that finely ground eggshells have a tendency to build up inside the pipes, clogging them with shell debris if you toss enough shells down the drain.
Better Garbage Disposal Cleaners and Sharpeners
Although eggshells may or may not work as a garbage disposal cleaner, you do have other options, one of which is ice. Ice can keep those grinders clean while eliminating any possibility of added buildup or clogged pipes. Drop a handful of ice cubes into the disposal and turn it on. The cubes challenge the grinders enough to clean them of debris and they melt, so there are no remnants left behind to clog the pipes.
Citrus peels also help keep disposals clean. While they won't sharpen a disposal's blades, lemon, lime and orange peels do leave behind a pleasant citrus scent. This is a natural and safe way to deal with a smelly disposal that won't damage the disposal itself or clog your pipes.
If You Can't Chew It...
Garbage disposals can handle a lot, but they do have their limits. A good rule of thumb is that if you can't chew it, neither can your disposal. Fruit pits and animal bones should never go near your garbage disposal. The same goes for shellfish. In this arena, size doesn't matter — even tiny olive pits are too tough for your disposal.
Other Garbage Disposal Do's and Don'ts
No matter what you put in the disposal, plumbers recommend that you rinse everything down the unit with cold water. Warm water has a tendency to separate the fats from some food waste, and those end up coating the disposal's grinders and walls. Fat deposits can also congeal further down your pipes, causing an expensive blockage you'll need a plumber to remove.
Stringy vegetables such as celery or lettuce grind when disposed of in small quantities, but large doses can leave a mess inside the disposal. Avoid starchy foods too. Potato peels, pasta and rice can all absorb water and swell up quite a bit. The result is a thick, gunky mess that can gum up your disposal and your plumbing.
The Ultimate Don't
Above all else, the most important thing to leave out of your garbage disposal is your hand. This sounds obvious, but it's easy to reach into the disposal for a dropped spoon without thinking. If you do need to retrieve an object from your disposal, use a pair of tongs, long pliers, chopstick or anything other than your hand to pull it out. If you do need to reach into the disposal, turn the power off at the electrical box so no one can accidentally turn the unit on while you're working.