So I'm reading that they are very messy eaters.
And they poop a lot.

How do you deal with all that poop?
Do you scoop it daily since it's pretty big and looks easy to scoop up?
Or weekly with the vaccum and water change?
What about the half uneaten pellets floating around?

I've adopted two 8 inch oscars. First 48 hours.

Well, what I do with mine, if there's alot of poop floating around and looks really yuck, I scoop it out. The one weekly water change, 25%, is to suck up the crap from under the substrate and ornaments. As for uneaten food, that is to be removed as it will just rot and cause the water to go bad!
Feed your O as much as he will eat but don't let it float around too long.

yup they r possibly the messyist fish on the planet.
as a general rule of thumb u nedd filtration rated double the amount of yr tank volume i find that three times more filtration works fine for me.

Defo need plenty of filteration there reall messy.But we love em.