IMPORTANT - to be able to use the blood tanks you need to successfully dodge the boss's purple attacks and get 3 stacks (so 3 successful dodges = 3 stacks, if you fail a dodge your stacks will not reset back to zero). Then after every zombie order mechanic the stacks will reset to zero regardless of whether you used it or not. You will be able to see the stacks as a buff stat under your character name in the top left corner of your screen.
IMPORTANT - to be able to use the blood tanks you need to successfully dodge the boss's purple attacks and get 3 stacks (so 3 successful dodges = 3 stacks, if you fail a dodge your stacks will not reset back to zero). Then after every zombie order mechanic the stacks will reset to zero regardless of whether you used it or not. You will be able to see the stacks as a buff stat under your character name in the top left corner of your screen.