A Faithful Reader requested a post on Sounding. This is a practice that began in the medical field for a variety of reasons, the primary of them to remove blockage from the urethra. And, of course for Catheterization purposes. Then it spread to the genital piercing technicians (think Prince Alberts) to assist in the opening, or expanding, of the urethra to help get the tools in that are needed to pierce through the head and place the ring.
Sounding for sexual reasons, of course, is because somewhere along the line, somebody enjoyed the sensations. Sounds, as they are called in the adult stores, can be made from many different materials: metal, plastic, glass... The length can vary: from very short (the length of the cock head) to very long (to reach into the bladder). Chuck Palahniuk introduced sounding to his readers in the short story "Guts," which appeared in the book Haunted.
The thing you need to remember is: safety. Never use a sounding instrument that might crack or break, and get lodged somewhere down inside your cock. And, never use anything sharp or pointed that might tear, cut, or perforate your cum-tunnel. Doctors have reported needing to retrieve all manner of things: batteries, pins, wire... Always use a something which has been designed for the purpose.
And, of course, always sterilize any sounding device before shoving through your cock. Infection is the most common side effect of the activity. If not caught and treated quickly, the infection can spread (and rapidly, I might add) to the rest of the genito-urinary tract: prostate, bladder, kidneys, seminal vesicles, and balls. And never, ever share a device without full sterilization.
If you like sounding, that's cool. Here at Big Whack Attack, we don't judge; we just want you to keep your man parts healthy. So, enjoy it, but be safe about it. Don't damage your dick for a few moments of pleasure-pain (pain-pleasure).