It's all about substitution. A collector can't watch you pee unless it's Military or Court Ordered!
Had my wife pee for me this morning. Took one of those 2 oz Energy Shot bottles and rinsed it out really well. On the way to the lab I picked up a cup of hot water from a gas station. I also brought a thermometer. I dipped the 2 oz bottle into the water for 7 seconds and it read 100 degrees. I then placed the bottle under my scrotum. I wore two pair of tighty whiteys so that it would stay in place.
Your body provides natural warming which is important because the lab tests that the temperature is between 90-100 degrees of the sample.
Since the collector couldn't observe I just emptied the bottle into the cup and that was that.
I even smoked a bowl on the way to the test and a celebratory blunt on the way home from the test!
Don't let a test stress you! It's easy! They can't observe so you substitute. I have smoked heavily for some time and know that dilution wouldn't likely work for me.