For this they have a special room. It's a tiny room with an examination table and a sink. The nurses say that when the hospital wing is rebuilt they are getting something more palatial. They have a serious collection of Black Label Penthouse magazines in carboard boxes. I had a subscription to this once. The local radio station was running a quiz asking how James Bond likes his Martini (shaken, not stirred). As I was one of the first 007 listeners to call in with the correct answer, I won two tickets to the latest Bond movie and a year's subscription to Black Label Penthouse. After about ten years they stopped pestering me about renewing my subscription. Unfortunately, sicko that I am, I don't find them arousing at all. The room also has a small wooden door. When you're finished, you can hand over your sterilised specimen jar through there. A buzzer alerts the nurses. I think they take it and freeze it in liquid nitrogen right away.
There are detailed instruction on the door. They want the sample produced by masturbation, not by any other method. Sex, even with a condom is right out. The part they are most interested in is the first, clear part but they want you to note what parts you got and what, if anything was lost.
They offer you twenty bucks for your trouble, which I didn't take.