It is my habit to change the brake fluid and clutch fluid at least every two years. The difference with fresh fluid can be surprising. The fitting that you asked about is equal to the fitting found on the brake caliper. I use a simple method to bleed air from the system or replace the fluid;
A short piece of rubber hose (3") that is tight on bleed fitting, a clear plastic hose that is tight in the rubber hose and long enough to reach a clear bottle or jar on the ground. Place the rubber end on the bleed fitting and the other end (plastic) in the jar with enough water or old fluid to keep the hose in the fluid. Remove the master cylinder cover, open the bleed fitting, and slowly squeeze the handle (slowly or it will squirt out!). You will see the dirty fluid coming out of the clear tube. Repeat until the master gets low on fluid. Do not allow the master to suck air!. Add fresh fluid to the master. Repeat until fresh fluid is coming out of the tube. Close the bleed fitting, top off the master cylinder, and reinstall the cover. Done.