I take off the lid to the brake reservoir, and push a brake piston thingy back, then look at the increased level of brake reservoir, and push another brake piston thingy back. At some stage, I normally have to remove some fluid from the reservoir with a dirty great syringe bought from the chemist for exactly this job.
You do not need to release pressure with brake nipple, the fluid magically finds its way up into the reservoir. And over the top if you don't remove some.
However, due to some track activities that the car participates in, I gnerally change brake fluid at the same time, since the car is already on jack stands and brakes exposed for bleeding.
Unless of course I'm in a hurry.