All About Dog Anal Glands - How to empty them and helpful tips

I asked my vet if she could explain to me what they are for and how they are emptied (expressed). She took 15 minutes of her time (much appreciated Dr. Luong) to educate me on the fascinating world of doggy anal glands.
Here's what she said:

What are Anal Glands

Anal glands consist of 2 tiny sacs (pea sized in my dogs) that are located just inside the butt of most carnivores (even cats) at the 8am and 4pm position for a total of 2 glands. Their purpose is for scenting the poo on it's way out and leaving a little scent on their behinds. Dogs are scent oriented and use this secretion to communicate with other dogs about territory, whether they're male or female and if they are in heat. Lots of info there.
So when dogs sniff each other's behinds, it's not the poop smell they're after, but the scent released from the anal glands.

As dogs were bred down to chihuaha sizes, problems with anal sacs increased. Smaller dogs are disproportionally more susceptible to anal gland problems than larger dogs.

Well this was handy a couple thousand years ago when they were wolves living in packs, and their survival could depend on knowing who's who, where they're at, and how they're doing.

Now, having domesticated and bred these same wolves into the dogs they are today, pack dynamics has changed in that they need to communicate with humans more so than dogs. We don't sniff their butts or poo and they don't (need) to sniff yours.
So their anal glands are rendered obsolete. Unfortunately these glands were never bred out of dogs. Maybe in a thousand years, dogs will no longer have these glands and we won't have to deal with them anymore but until then it's either trips to the vet, the groomer, or to our own bathtub..... next emptying dog anal glands

on another note, sometimes training can be challenging....