No, you do not need a garbage disposal to have a dishwasher. A dishwasher will work without one, and while it's rare to see a home with a dishwasher that doesn't have a disposal, it is possible. The two appliances pair well and are often installed together because a disposal simplifies meal cleanup.

However, your dishwasher should not be used as a replacement for a garbage disposal. Subjecting it to continuous food leftovers can lead to major clogs. If you choose not to install a garbage disposal, you should thoroughly rinse your plates or scrape excess food into the trash or a compost pile before loading them into the dishwasher to prevent plumbing issues.

Your garbage disposal is not draining because it might have a clog due to food waste, a foreign object, grease, oil, fat, or it may have a broken motor. When water doesn't flush out of the disposal, that's a key sign that your disposal has a clog or needs repair. 

On average, a garbage disposal can last anywhere from 7 to 12 years, with many models functioning well for about 10 years. With heavy usage, a motor may last a minimum of five years, while grinding plates will wear down over time. It's generally a good idea to consider a replacement if your unit is approaching the 10-year mark. Other signs that it's time for a new disposal include frequent leaks, persistent clogs, lingering odors, lack of power, or unusual noises. If your unit is not that old, it's worth investigating if a less expensive part, like a rubber seal or a loose hose, is causing the issue.

Most garbage disposals have a reset button that can be triggered with a tool as simple and accessible as your index finger. That said, if you need to perform a more in-depth troubleshooting step, like manually moving the arms inside the unit or rotating the impeller plate, a hex wrench is the most common tool you’ll need. Most garbage disposals come with a hex wrench.