impossible to test positive..
even if it was old bud and decarbed naturally at room temp. even if you snorted a line of sift (logp of the drug doesn't really let this be effective)
think about this logically..
say you somehow inhaled a shit ton of vapors.. it gets absorbed and enters your blood stream, (say smoking an actual joint, in roughly 10 min peak concentration occurs at roughly 150ng/ml... ) its now being circulated through your body. it doesnt just stay circulating. without getting all fancy, obviously some crosses blood brain barrier it gets metabolized and excreted in feces, urine sweat etc.. eventually-within ~8-12 hrs none is left in your blood
in this time frame metabolites are building in your urine
thc then has a half life (terminal not really mattering here) in your body.
for example 20mg doses of thc orally over a period of several weeks as in marinol are unlikely to test positive beyond 118hrs.
if you smoked half a gram with an avg of 20% thc of dank bud last time you smoked
(.1 grams of thc)
with a bioavailability of about 20% through smoking .. only 20mg of thc entered your body.
you can pass a urine test smoking in a couple days
and doesnt take days for it to show
if you feel like edumacating yourself
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2689518/