One caliper is connected to the other I believe from memory. I'm bleeding both.
No nipple on the master cylinder
Sounds like the same setup as mine then. When my friend in the trade bleeds mine he clamps the line that goes from the 1st caliper to the 2nd and bleeds the 1st. Once all air is removed from that one tighten up the bleed nipple on the 1st caliper, remove the clamp and begin work on the 2nd one. The top is completely off the reservoir while this is being done.
If you are not clamping off the other side I would recommend starting there