Oh by the way its not just your piss you need to worry about, one guy with my husband at Raleigh was binned - he passed the urine drugs test but when they brought a sniffer dog round the dog started going crazy and barking at his pillow - weed stays in your hair for months and months and months - then tested his hair and its was close the door behide you.
Also on submarine training a guy was binned due to having weed in his car, again passed the piss test, but failed a hair one. He was discharged after 2 years of highly expensive training.
At basic they didnt have a urine test for 6 weeks (from starting point) so make sure what you did before didnt show.
Cannabis will stay in your system for around 30 days if you're a regular user and much less if it's been a one off. Be aware too that if you take co-codamol for a headache you will test positive for opiates on the multipanel. If the sample is sent to the lab then there will a breakdown of the opiate (e.g. morphine, codeine, 6-Acetyl Morphine). Not a lot of people know that! I work in addictions so I know about such things! You will not be drug tested at selection, your urine will be screened for the presence of nitrites/leucocytes/blood/protein/glucose and so on as this could indicate a number of physical problems. Provided you don't use for a period of more than 30 days then there will be nowt to worry about.
Okay... Common sense tells me not to use the bleach idea, however the caustic soda, ive never heard of and wouldnt have a clue where to find it. The vinager method could work though. Ill bare that in mind.