Can they tell if you use someone's else's urine when you go for a drug screening?

How are you going to keep the urine warm when you go for the test and how are you going to hide it? That is the main question here. And why do you need to use someone else's urine and not your own?

Some testing places make sure you are using your own urine as they watch you go pee. Other places make sure you don't take anything into the stall with you other than the collection cup.

There is a gauge that shows if it is within normal internal body temp. So as soon as you use room temp urine they will know. ( at least in every test we ran)

In other places, they actually watch you urniate.

And I will agree with twinkie here , what you are asking is how are you going to cheat on a urine test for some reason. I will assume a drug test?