If I have a garbage disposal, can I pour grease and debris down the drain?

No, grease should never be poured down the drain. It will solidify in the pipes and can cause a backup in your lateral line. It can also cause problems at pump stations and at the sewage treatment plant. Even if you have a garbage disposal, you should scrape all solid particles of food off your dishes into the trashcan prior to rinsing them in the sink.