Trouble Bleeding Rear Brakes, Rear left one is fine but nothing comes out of rear right Options

[LTom]

I recently overhauled both rear calipers and now i've put them back on they require bleeding. With the help of a friend who did the pedal pushing I first bled the rear left (passenger, uk) caliper which went fine. However the rear right one just will not bleed. Nothing comes out as far as I can tell, not even air. I have taken the bleed nipple off and it is not obstructed, i can blow air through it. What the hell is causing this? I'd really appreciate some help as the weather is grim and my only other means of transportation is a motorbike.

[Special_Edy]

This is part of why its suggested to take a section of hose(preferably clear), plug one end over the brake bleeder nipple, and submerge the other end in a jar partially filled with brake fluid. You will see if air or fluid is going into the jar.

I'd verify that the brake fluid reservoir isnt losing fluid while you attempt to bleed the problem caliper(would indicate a leak) and check the brake line for kinks or bends.