Don't start doing it unless he dog scoots. It's actually the anal sacs (not the glands themselves) that get full - they just store the liquid produced by the glands.
The sacs are at 4 and 8 o'clock in the anus, and they usually get squeezed easily when the stools are a good consistency and the contents are liquid enough. If the stools are soft or the contents thick/grainy then they can impact and the glands need to be emptied.
So normally unless your dog shows discomfort or scoots/licks, don't touch them... Doing them when it's not needed isn't very useful.
My sister's beagle had numerous anal gland abscesses that bursted, she thought of having the glands removed cause they were so problematic but there is a big risk for fecal incontinence afterwards, and with metamucil in her food daily things got better...
Also groomers tend to do it from the outside (squeezing the area where the sac is like a pimple) - not only does this not fully empty the glands but it can also cause some damage to the sac itself and sometimes cause problems. You really got to get a finger in there.
“Your birth is a mistake you'll spend your whole life trying to correct.” Chuck Palahniuk
I love pus but I hate people.
I can say words like undifferentiated gonads now!