there arn't fish that will eat the waste of other fish but amano/japonica shrimps are detritiovors and will clean round the tank. just make sure that there are no large or aggressive fish.
There are no fish that you can expect to do that. If you are wondering about this because your tank is getting dirty, you will have to clean it out yourself using a siphon, which is a simple enough thing to do. Here's a link that discusses it:
If you are wondering about it because you are thinking about getting some fish to live on the lower level of your tank, corys are IMHO, the best. Here's a link that shows the many kinds available:
I already have a siphon ,but the patties crap so much that i feel like doing it every day .. Of course i cant do that ,but you know what i mean.... All the same i was just wondering .... thanks anyway
Maybe you could get an undergravel filter. Do you have a filter? If your tank is properly stocked and has proper filtration platty poop shouldn't be that big of a deal!