Well, as mentioned the drow 'burials' is a long forgotten tradition which is no longer practiced. As actually it is<em>shameful</em>for a drow to die by old age. As otherwise elders are wrapped into spiderweb cocoons and let to hang upon house entrances and they are kept in there until they rot completely away (as removal is considered as a sin which offense is met with death on altar by Lolthites). True there could be super ancient catacombs with first matron mothers but your lucky if you find more than bone dust in there. As usually present ways how bodies are dealt with is drop them feed the spiders and some species eat even bone. Funerals are held sometimes but what I understand because of varied necrotic practices the bodies are disposed. Not so carefully with other species in the city but drow bodies are very well removed if they are not commoners or freshly died by old age. Or bodies result of clumsy murders as murderers try hide the bodies if they cannot dispose them properly.