The brake line from the rear brakes go directly to 1 reservoir of the new MC. The distributing valve has 4 holes (1 for front left, 1 front right, 1 rear and 1 from MC). You are basically removing the 1 line from the rear brakes and going directly to the MC (that's the hole you plug (on the distributing valve)). Then you're just putting the line that goes from the old MC and put it into the new MC. 2 lines now are coming out of your new MC, 1 going to the rear brakes and the other going to the distributing valve for the front brakes.
