Help bleeding brakes

Can anyone tell me how to blled the brakes on a I series 325 BMW.

A friend of mine is working on one. No rear brakes. No fluid to rear brakes.

I think it's the proportioning valve. He insists it's how to bleed the brakes.

well how you are supposed to bleed the brakes or how i do it is get an empty container and a small rubber hose that fits over the valve that the fluid comes out of and pump your brakes until the pedal wont press then have a second person or buddy loosen the valve and out it comes and into the container tighten it again pump the brakes and repeat that about two or three times or until it flows smooth without any bubbles coming out. and repeat with each tire. but then again thats what ive done on most vehicles never done it on a bmw though