Filthily
/ˈfɪlθɪli/
Definition 1 of 3
Pro Tip 1/3Extreme Uncleanliness
Use 'filthily' to stress very poor hygiene or messiness. 
His clothes were filthily stained and smelled terrible.
Pro Tip 2/3Negative Emphasis
'Filthily' conveys strong disapproval of cleanliness standards. 
They ignored the filthily muddied floor of the restaurant.
Pro Tip 3/3Physical Environment
Often relates to one's living or working conditions. 
She had to work filthily amidst piles of waste material.