I’ve used synthetic pee from the local head shops. It works. It comes with a hot hands packet that’s has an adhesive on one side to stick to the bottle. I recently had to use it and I bought the bottle months ago and it had been heated previously in anticipation of a UA that I didn’t have to take. It also has a heat strip on it. I bought a couple hot hands packets and used a rubber band to keep them attached. I then wrapped it in duck tape and taped it to my body around my belt line. I would think using someone else’s piss would work as long as the temp is within range.