take it from an experienced person, try until it comes out perfect. use children or small rodents as test subjects, then strap a hospital mask that's attached to a gas can. next, pump the gas into the tank, and onto the mask of the first lucky subject. if it dies instantly, you know you're good, bud don't stop there. You ACTUALLY succeeded if it takes longer for the subject to die because you've caused max pain and suffering. Good Luck.
P.S.
if you run too many test and run out of subjects, I recommend the nearest daycare, they're pretty easy to raid.