- Grease and other fats. These can cool in your drain and eventually clog it.  - Egg shells. These have a filmy membrane that can wrap around the moving parts in your disposal and cause problems.  - Animal bones. These are too hard for your disposal to break up and can cause it to lock or break. - Coffee grounds. These can settle to the bottom in your plumbing, eventually causing a clog.  - Pits and seeds. These are often too small and hard to break up well, so they can get stuck in your disposal.