Complex sentence: Odin, posing as an old man, advises Sigurd to dig trenches also to drain the blood, and to bathe in it after killing the dragon; bathing in a dragon's blood confers invulnerability.
Split into simpler sentences: Odin, posing as an old man, advises Sigurd to dig trenches also to drain the blood. Odin advises Sigurd to bathe in the dragon's blood after killing the dragon, telling him that bathing in a dragon's blood confers invulnerability.