I've had to do Harvey a few times before. The vet was happy to show me how (I was getting a bit fed up with paying £16 for something I could do myself!!)
Because of skin problems Harv has to have a bath once a week, and so I routinely check him bottom (only other dog owners would understand this!!!), and when he is all soapy it is an ideal time to empty his glands.
I have to say though that he has been on Chappy for the past 4 weeks, and so his poo is firmer, and his glands have not needed any attention - something that Harv is very happy about.