Dumping spot for human and animal corpses. Each grave can be set to individually accept or deny strangers' bodies, colonists' bodies, animal and mechanoid corpses.
When idle, colonists can visit graves to gain joy.
Putting colonist bodies in graves instead of dumping zones will prevent the "Observed corpse" and "Colonist left unburied" unhappy thoughts.
Alternative solution to using graves
Define a Dumping zone somewhere (preferably under some kind of roof), set the dumping zone to only accept bodies, when there are bodies in the dumping zone, draft a colonist and equip him with a Molotov cocktail (or a frag grenade) and throw it at the bodies. If one body catches fire it will spread and incinerate the others (the roof prevents the rain from extinguishing the fire).
Using a butcher table add a bill to butcher the corpses. This will not only get rid of them but also provides you with meat and leather. Be careful, butchering human corpses will grant the " Butchered humankind -6" debuff for the cook and the "We Butchered humankind -6" debuff for everyone in the colony, as well as affecting relations between the chef and other colonists. Note: this only works with non-rotten corpses. Colonists with the Psychopath, Bloodlust, or Cannibal trait are unaffected by the debuff.