I know it has been asked many times, how long it shows up for, but I need to know a more different question. Say if I was clean, then smoked a joint, how long before my urine is going to show up as dirty for marijuana? Doesn't it have to go through your system before it gets into your piss, and wouldnt it have to metabloize or something? I was thinking at least an hour to afew hours, but maybe longer? If anyone knowshow long before it does show up if you are already clean,I would aprreciate it.