Of the four cauldrons in the Western Plaguelands, the one at Felstone Field may be the easiest one to gain access to.  The Scourge have greener troops positioned here, though they should not be underestimated.$B$BGo to Felstone Field, due east of here and northwest of Andorhal, and engage the cauldron lord there.  On it is a key that will unlock access to the cauldron.  When unlocked, use this bottle to get a sample of the cauldron's toxins; we'll need it for study in developing a counter agent.