I've forgotten the title of a novel I was reading. It started out with the MC being captured and brought to some demoness sect where they were going to rape him to death to extract his yang energy. There was a girl there that give him a bead that ended up being a powerful artifact. An old man showed up and wiped out the sect and took the MC as his disciple after the MC used the bead to absorb one of the black fire dragons the old man used to wipe out the sect. I think the master was referred to as "old monster" or something by his enemies and had a big cauldron he'd use to flatten people and send out black dragons to attack with. The MC ended up learning some method to dual cultivate in a manner that enhanced both cultivators instead of one person extracting the energy from the other and crippling them. EDIT: @Daken Thank you! It's Grasping Evil.