hmm 21 days is still a little soon, but you may be okay. if it is your recruiter giving you the piss test dont worry, even if you have weed in your system at the time. trust me they will wait until it is out of your system. if your going to MEPS to take the piss test, idk why your recruiter would send you up there if there was weed in your system anyway. just keep drinking a lot, a lot of water. stay hydrated and youll be fine. good luck