@Vah urethral sounding is not something you want to get wrong as it can cause sever and permanent injury to your urethra. The first bit of advice is the need for complete sterility , the development of a urinary tract infection ( UTI) in men can lead to sever sepsis. Men tend to suffer more when they develop a UTI and often get admitted to hospital. So if you are prone to UTI's then its is not recommended to perform urethral penetration play
So you would need to use sterile lube . Next the actual sound either metal or silicon should be boiled should be left to simmer for 10 minutes between uses.
As a newbie you should choose a flexible, medium-sized sound. Until you're practised in this play, choosing something too rigid or too slim can increase your risk of puncturing the urethral wall.
Using a toy which is too thick is just as risky as using one which is too slim. Listen to your body and take it slow while deciding the right size for you.
If you feel a sharp pain or that one particular area hurts more, stop immediately.
You may experience some burning during urination for a few hours or day after play (especially the first few times). This is normal, but you may like to use more lube next time. If these sensations continue for more than a day, seek medical attention.
If you experience unusual discharge, heavy bleeding, fever or cramping, seek medical attention.
This is something like I said at the start that potential cause permanent injury to yourself , so think carefully and proceed slowly.
Hope this helps
RN