If proper protocols are followed in regards to D/O collections, the observer (who must be the same gender as the donor - no exceptions) must enter the restroom stall with the donor and directly watch the flow of urine exiting the body and into the sample cup. Its right then and there that any artificial delivery systems are spotted.

In observed DOT tests, the observer first instructs the donor to raise shirts and lower trousers and showing the observer, by turning around 360 degrees, that the donor is not possessing any artificial delivery devices. If a donor is caught with such a device, the observer informs the collector, who stops the collection and declare a "refusal to test".
This can also occur in some non-DOT situations as well.

Just practice and make the effort to keep the sample temp within proper range. Then you dont have to worry about the humiliation and dehumanization that surrounds collections and re-collections under D/O.