i used to have to do this to morgan every week during her shower. I do it from the outside as well. Even though i'm a tech i just cannot stick my finger in her butt. LOL its too small and i can't get a good grip with my pinky finger.
So here is what i do. Luckily Morgan will just stand there while i do this. I put her so that she is facing me. I lift her tail with my right hand. Then with my left hand i put my thumb at 4/5 o'clock and pointer finger at 7/8. Next squeeze and "pull" outward. You are trying to get behind the glands and squeeze the goo out the butt. Once i'm done i quickly put shampoo on her butt and let it sink in to get the smell off.
i hope my description makes sense. You are NOT going to hurt him doing it this way. Don't wimp out if he whimpers a little. he's probably just trying to use the 'poor me' whine to get you to stop. its going to feel weird to him because its probably never been done before.
You can do it!!!! Just go for it!! hehehe
