2005-10-01 : If the third ability triggers, removing a counter in response won’t stop the effect. However, somehow removing Plague Boiler from the battlefield in response would stop the effect because then you wouldn’t be able to sacrifice Plague Boiler.

2005-10-01 : The sacrifice is done on resolution of the triggered ability.

2005-10-01 : You choose whether to add or remove a counter when the second ability resolves. You can’t choose to remove a counter if there isn’t one there.