The Machete Twins Lyrics

Lyric discussion by Roone 

Cover art for The Machete Twins lyrics by Pig Destroyer

I love this song, too. But the only thing I don't get is the part with "shallow graves". What do they need the graves for? First I thought, they kill someone, take his money and "add" the corpse into another persons grave. But then it says "they leave his carcass by the reservoir". Any explanaitions?