
Unless they do need draining for some reason, leave them alone! I can drain mine, but I never go inside - just push at just below the anus on both sides. If they are working ok, there should be no need to be draining them. If they need to be done, a vet should do this unless you are experienced. and he needs to be involved to see what comes out and whether it needs treating. These glands are never meant to be empty, letting a small amount of the 'fluid' in them with the passing of each normal stool. During periods of diarrhoea or looseness, they may become clogged/infected however, in which case they would be packed with antibiotics.
As they will refill, you need to look at the dog's diet, so his stools are normal especially if they are continually being impacted.