It's easy to run the rear res. dry while bleeding. The only way to see the rear res. level is to look at the inside very rear of the res - about the last quarter-inch. In addition to filling the res. to at least the bottom of the fill port you need to rock the res. back and forth to get it past the baffle and into the rear res.

Do this while watching the inside very rear of the res. to be sure you are getting fluid into the rear portion of the res.

Duke