this is how we learned... just as most things these days youll learn from youtube

go figure,,,,,, but after you decide on the most proper way of the initial insertion,,, simply insert the right sized probe until it wont go anymore,, remember, this probe should be lubed up,,,so as one could imagine,,, it will slide freely

. so when it stops, thats it...theres no need to force it any further.. to me,, that just seems the more safer of the two (unless you just want to "squeeze like toothpaste" or take chances on prolapse, or worse.). that being said,,, there are some pros that take pride in poping with one hand.. whatever you feel most comfortable with.
just my thoughts
spooky