The Waste Removal Charm is used similarly to the Scourging Charm, but instead of cleaning off an object it seems to be used more to vanish litter. The first years learned this spell before they learn Scourgify, meaning it may be easier to cast, or may simply be a more generic/less precise version of the Scourging charm, where it just removes things entirely rather than making them cleaner. Hermione was shown teaching other Ravenclaws how to use this spell. She notes that she only needs to crumple the paper up to be able to use the charm, but thinks that splattering it with ink and dirt will help the other kids succeed easier. This makes it seem like the spell's effectiveness depends more on how the user perceives the rubbish than on how dirty it actually is, though dirty itself is somewhat of a relative term since there's no standard with which to hold trash to. It is interesting that Harry never is shown experimenting with this concept when just a few chapters earlier he was utterly convinced that it was wizard's preconceived notions of spellcasting that affected what they cast rather than the execution of the spell itself.