You'll find me clean when something is full,
But mix me up and I'll brighten a room looking dull.
Down a size, I'm one you'd never hire,
But shuffled again and I'm shared 'round a fire.
Reduced once more, and later your insides may ache,
But reworked again and it's your thirst that I'll slake.
Hopefully you didn't have too much trouble solving it. Any and all feedback is welcome!