I'm having a little trouble with this seemingly easy task. i open the bleed nipple and attach the mityvac. the problem is, the bubbles never ever go away. shouldn't the brake fluid be coming out without bubbles? maybe the tube is not tight enough around the nipple? maybe the nipple is too loose? help! i've never bled brakes with a mityvac before. what am i doing wrong.

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$500 1982 240d owner "Gunter"
125k miles,4 speed manual
crank windows, MB Tex, all original
no a/c, daily driver
Scorecard so far....
$230 Maaco paint job
$27 dimmer switch, $40 shutoff valve, $45 brake MC, $260 calipers, $40 brake hoses, $40 side fender trim, $20 balancing, $109 lifetime alignment, $10 fuel return lines, $115 oil&fuel filters for next 30k miles