I presume it is a pure that has been leveled up on the road to get 80 Dung. I.e. you start dung when the account is fresh, and by level 80 you have X stats, with 1 Def or something.
EDIT: As for the value I dunno...It is worth the time spent botting it, there are account sellers on Sythe that bot up accounts via Dung then sell them so it must be good.
Dung. Pure could be anything to do with dungeoneering, . I'd say a gravite 2H F2p Pker would be a great Dung. pure. 45 att, 63 dung, and the rest of the combat exp going into Str. You'd do work on kids.