AS ABOVE WHEN U BLEED THE REAR BRAKES U HAVE TO BLEED THEM WHILST THE CALIPER IS NOT FIXED !
SO U CAN PULL THE CALIPER ROUND TO THE TOP SO THE NIPPLE FACES UPWARDS THATS HOW ITS EXPELS THE AIR GIVE IT A TRY IT WILL BE THAT!!

YOU'LL NOT BE GETTING THE AIR OUT OF THE RAR CALIPRS!