Several ways exist to do this.
Original tried and tested requires two of you - one to pedal the foot brake and push through the fluid to each wheel in turn as the other opens and closes the bleed nipple with each foot press till clean fluid emerges into the waste bottle/cup/bowl, or whatever you choose to collect it in.
Tried a Gunsen Eezibleed system but that was not good. It relies on tyre pressure to force air through from the foot brake reservoir. The cap did not fit properly and I ended up with brake fluid spilling everywhere. Correctly used with much-reduced tyre pressure it might work but I lost patience with the ill-fitting cap provided.
I now use a Sealey system (Model No: V5820.v4) and it works well. The pressure cap fits well onto the reservoir and there is a gauge to tell you the right pressure to use and full clear instructions. A large sturdy bottle incorporates a pump to pressurise the fluid through the system and a relief valve to de-pressurise before releasing the cap onto the reservoir so reducing the likelihood of spillage. The bottle/reservoir is large enough to contain all the fluid required to do all four wheels eliminating the need to keep topping up.
There are other systems that rely on sucking the fluid out via a vacuum pump but I have not tried one of those.
Top tip = Ensure reservoir is re-filled frequently during the proceedings, to avoid air being sucked or forced through the brake lines. Otherwise, it means starting all over again to get rid of every little bubble.

Not for human consumption - Wash hands afterwards!