I use a clear tube attached to the bleeder screw. You can see the difference in new/old fluid as it moves through the tube. Added benny to the clear tube, you can see any air bubbles as they push out with the fluid.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.