Master cylinders have 1 or 2 holes?

Every cross cut diagram explaining master cylinders shows 2 fluid ports into
the piston bore.
After disassembly my Yamaha's Nissin unit has one very obvious hole down the
center of the reservoir, and another hole machined at the edge of the
reservoir's base that doesn't seem to go anywhere. There's no corresponding
hole in the bore.
Is that it, 1 hole to clean out?

 

There should be a fluid hole allowing fluid to go down into the piston
as well as a tiny air bleed hole to allow trapped to rise up into the
reservoir...

If the air bleed hole gets blocked up with crystallized glycol, the
brake lever will get very hard as heat builds up pressure and the
brakes will drag...