Once a quarter.
I go to the downtown clinic; and yes, I really stand out (no tats, over 30, bathe, etc.). I choose the clinic because I calculate the PA sees up to ten STD's a day, and he'll be able to spot the most subtle sign when he does my physical exam.
Never tested positive for anything. Wish there was a way to get an accurate statistic on how many hobbyists/providers did test positive and for what. I agree with previous poster: I imagine the number is low compared with sexually active civies.