Bench bleeding flushes out all the manufacturing grease and dirt, otherwise all that stuff has to flow through the entire brake system. Bench bleeding is nothing more than using a dowel or phillips screw driver to push the piston in while the mast cyl has fluid. With a few pumps your done and all "Primed up". Yes, you can buy the speciality tool lines to flow the line outlets back into the master cyl reservoir or just let it flow on to the bench shop towel.

Normal Brake Bleeding procedure
Install the master and reservoir, pressurize the brake system using a brake tool, bleed out the RR, turn on the Foxwell or other activation software tool, cycle the "ABS Brakes Solenoids" that will open up all the passageways in the ABS block, run the systems test and PRESS the brake pedal 5 times with the entire set up still attached. In other words, pressure on master cyl, fluid full in master cyl, caliper bleed screw open, catch can in place, ABS finished cycling, pump pedal 5X. More to LR, RF, RR. Repeat one more time until all fluid flow is without ANY bubbles.

Road test

Rebleed one last time using all the steps.

Done put away the tools and clean up.

Anal? Yes but it works every time.

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2005 X5 4.8IS
The Blue ones are always FASTER....

Current Garage:
2005 X5 4.8is
2002 M5 TiSilver
2003 525iT
1998 528i
Former Garage Stable Highlights
2004 325XiT Sport
1973 De Tomaso Pantera, L Model
1970 Dodge Challenger T/A 4 sp Alpine White
1970 Dodge Challenger T/A 4 sp GoManGo Green
1971 Dart Sport, “Dart Light” package
1969 Road Runner 383
1968 Ply Barracuda 340S FB Sea-foam Green