I wouldn't use a condom,they break to easy. Pickup a small travel bottle of shampoo thats 2 to 3 ounces and flush it out thoroughly. Nuke it for about 10 seconds and store it in your crotch. You really need a digital thermometer or something to help make sure the temp is staying correct. I wouldn't use anyones urine that is on prescriptions. Some will show a false positive for other things and then you have to explain to MRO why you're positive for something you don't have a prescription for. Subbing with synthetic urine would be much better.
Dillution depends on how much you've smoked over the last month or so. If its just a blunt or 2 a week dillution may work but you really should test yourself at home to be sure. If the jobs important to you spend a couple bucks to insure you get it.