Get someone to assist you as you will need to build up a bit of pressure. What you are experiencing is nothing unusual so don't be alarmed. Get a mate/missus etc to hold the spanner, bleed tube & bottle. Pump the pedal up/down by hand until there is a bit of pressure, hold it down and get mate to open the bleed nipple, keep pedal down/lock nipple, etc etc. It will improve and 99.9% of time will just take a little perseverance. [Sorry if most of that is egg sucking but no point half explaining]
Have you checked that there is no other bleed nipple in the circuit ? Some systems have more than one, when they employ a booster circuit ?
I have also had to go to the extreme of having to bleed the system by releasing the pipe from the master cylinder and pumping/bleeding from there to get fluid out, then moving through the remainder of the circuit.
As a tip for the future, when removing slave cylinders for operations which don't necessitate it's bleeding, tape the pin into the slave to stop it from falling out, keep the whole circuit intact and tie it up in the engine bay then it's not necessary to bleed it. If you still desire to do so, you are bleeding a full system, not an empty one.
