Not only will throwing a bile bomb on a Tank get you an achievement, but it's also a strategically smart move, because the common infected will attack the Tank for you. You'll know if you hit the mark because the Tank will be outlined in purple, just as you and your team members are when they're covered in boomer bile. Wait for the Tank to rush you, or until it's climbing a structure, which will increase your chances of hitting it.
You can find the Bile Bombs at random locations in each level, and on CEDA agents in the Dead center campaign. CEDA agents are the enemies that wear the large hazmat suits. Remember that the suit allows them to pass through flames, including those produced by molotov cocktails.