If I'm not going to reuse my yeast I just flush it; I don't have a garbage disposal otherwise I would do that. I think it's good for the environment as well, more yeast in the sewage system to break down...unmentionables.
But why not re-use it? If you had a healthy fermentation, you can just jar up the slurry in a sanitized mason jar, refrigerate, and use it for your next batch, without washing (which I agree is a PITA). Especially if your next brew has a higher SG than the current one, you're starting with proven yeast that will take off fast and finish clean. Or just use half of it. I do it all the time and never have issues, as long as I keep track of the generations and never go over four re-uses.