I had this done by a girl, Rose was her name, at 197 Clarence St some years ago. Her suggestion. It was extraordinary, it feels like you're oozing rather than spurting (apologies for the terrible description). I had it several times and she seemed to specialise in it, given her adeptness and advice on how ro relax. Essentially that boiled down to having an empty bowel and therefore no worries about shit on her gloved finger.

She also seemed to enjoy doing it which helped me feel more comfortable. The other advice is to have full balls - maybe 3-4 days worth. This helps you feel as if you're cumming forever. Quite extraordinary.

One of my current regulars finishes me off like this while deep-throating me. It is simply the best way to orgasm i've ever experienced.