Recommended liquid: SAE J1703 (DOT3).
On the cylinder of switching off of coupling weaken the union of pumping and attach to it a hose. Arrange other end of a hose in glass capacity of sufficient volume.
Slowly press a coupling pedal.
At the pressed pedal of coupling weaken the union of pumping and let the air out from hydraulic system. Tighten the union of pumping and release a coupling pedal.
Repeat operations until there will be a brake liquid without air vials.