Let’s start by debunking a common folk remedy. While it’s true that dropping coffee grounds into your garbage disposal reduces odors in the short term, it can actually cause more serious problems down the drain. To understand why, think about what used coffee grounds look like when taken out of a filter: They reduce into a dense, thickly packed pasty wad. And that is exactly what you don’t want going in your drain lines!
Leave the grounds out of your disposal, and use them to keep critters out of your garden instead.
Anyone who’s made spaghetti or mac’n’cheese knows that pasta expands when soaked in water. Given that, you can see why you might not want to drop lots of pasta into your disposal and drain where it will, after all, soak in water and keep expanding.
Like most of the items on this list, a few scraps cleaned off of a plate won’t hurt. But don’t try to dispose of an entire pasta casserole, and when you do run pasta through the disposal, run the water as cold as it will go for 30 seconds afterward, to flush it through the trap and into the main line. Otherwise, you’re likely to run into clog issues, as this firsthand account will attest.