Catheters in a hospital go pretty far in, remember that from the anatomys standpoint the ureter goes farther inside the body than just through the penis
And if you ever go into a sex shop or lokk at the sex toys on the internet you probably see things like that. People are weird believe me :)
The deepness is particularly safe, but the fact that he licked it before putting it in is the unsafe part. It should be cleaned properly or else, infection to sensei's cute dick.
it's called sounding. You can learn how to do it safe.
from a realistically physical and medical perspective, is it possible to insert the catheter THAT DEEP?! Is that SAFE?!
I always thought it wasn't inserted that deep