In regards to the urethra one of my favorite forms of CBT is to have Tabasco sauce poured in it. This has been done close to a 100 times with no lasting ill effect. It only burns a little at first (I am guessing that the semen already inside has a moderating effect) but it steadily intensifies until it reaches a peak then slowly subsides.

One Domme decided to improvise and coated my balls with it as well which caused extreme nausea and I ended up vomiting which as someone noted in another recent threat is very gross. Needless to say the session ended early.

There was another Domme who worked at Nutcracker who loved doing it to me. She would often invite the other Dommes into watch. Usually when a Domme summons an audience it is to entertain the sub but in this case I really believe it was to give her colleagues a treat.

There was one instance where she improvised by trying another hot sauce. I am guessing she was hoping it would be a notch more painful. Actually it was less painful in the urethra but after a while I began to feel it in my balls. I started to feel nauseous. I didn't vomit this time but came close and again the session ended early. The Domme said she felt bad. Up until then I really liked her and forgave this miscue as an honest mistake. We continued to session until she left for the West Coast.

This incident warned me that it probably wouldn't be wise to experiment with harsh chemicals in the urethra and I've stuck with the Tabasco ever since.

YMMV

After that I had a session with another Nutcracker Domme and requested this torture. She had been in the audience before and said I had become famous at Nutcracker. She said she tried it out on another very masochistic customer who was a "tough cookie" and it "broke" him.