Sometimes the bleeder fitting will suck air and give you bubbles if you do a vacuum bleeder. Sometimes the hose on the bleeder fitting will not be 100 percent sealed and suck bubbles. Also, the fluid always looks crappy as it is.... however old. I just recently went through this with my ranger trailer when I replaced the front actuator. I am super ghetto so take this with a grain of salt. My bleed method was pump the actuator several times with a screw driver, and then i put a bungee cord on the screwdriver to keep the actuator.... actuated? Then I went to the back and opened the bleeder and let fluid spray until the fluid stream slowed down, then shut the bleeder. Then start over. Did this about 10 times a side, all of the old crappy fluid came out and it was flowing clean. Start on the furthest side first. Had no issues, took maybe 30 minutes from getting the new actuator bolted on till the brakes worked. The clunk was driving me insane so I had to fix it.