Domina Victoria Rage has a very informative post up on the subject of sounds. If you’re thinking of trying this type of play, it’s well worth reading.
I’m always surprised by how a lot of guys react to the idea of sounds. It’s often described as edge play, and seen as an intense masochistic activity. In reality it’s a very sensual and stimulating sensation. If it’s painful then you’re doing it wrong and should stop. As Domina Rage says, the idea is to let gravity do all the work. The sounds is simply supposed to slide in under it’s own weight. Nothing should be forced. Both the invasive act and the stimulation of the nerve endings makes it very enjoyable.
I’d add just two things to Domina Rage’s post. Firstly, drink some water beforehand and pee afterwards. That’ll flush out any lube left in the urethra. Secondly, don’t assume penis size is related to urethra size. I think I’m relatively well endowed, but I can only accept smaller sounds. I’m always amazed what some guys can take when I look at the range of sound sizes. Start small and experiment to see what works for you.
Both images come from the CBT and Ballbusting site.