Oscars are so messy, I used to keep my pair of oscars with a Lima shovelnose. 50% of what the oscars ate comes out of their gills, and the catfish ate all of it. I recomend Lima shovelnose they are peaceful and fun to watch. Syno´s are good at cleaning at first but they get lazy. I had one that got huge and just sat in a cave all day, he also got really aggressive as time went on. he was the featherfin variety.
Right now in my 225 I have a single sun catfish thats doubled in size since I got him. this guy is ALWAYS fat. he eats non stop keeps the gravel clean and to clean the glass I have a flag tail Prochilidus who is munching away at everything 24/7.
My champsochromis Caeruleus puts a cloud of food out from his gills when hes trying to swallow about 7 pellets at once, but the other fish go mad for it, my GT eats it all up and so do the 8 columbian tetras I have. they started as dithers and cycle fish but they are great at keeping the food eaten.