Before you install brake hoses on the calipers, put brake fluid into the calipers until they're full, and then install the brake hoses. If your master cyl was empty because the brake hoses were disconnected from the calipers, now put brake fluid into the master cyl. If you use a MityVac you should be able to get brake fluid entering the MityVac very quickly. Keep an eye on the master cyl fluid level, and fill it before it goes empty. If it goes empty, you need to start with a full master cyl, and begin to siphon the brake fluid from the caliper bleeder nipple, again. The empty master cyl introduced air into the brake lines, and you need to work the MityVac until you only have brake fluid and no air in the MityVac line & reservoir.
If you use a reverse-bleed, you do not need to put any brake fluid into the master cyl. It can be empty. Why? Because using the syringe, you are pushing brake fluid into the empty brake lines, and then, into the empty master cyl. In the master cyl, as it fills with brake fluid from you using the syringe (pushing the plunger IN), you will see the bubbles in the filling master cyl become smaller and less frequent, and then, no bubbles. Now you should be able to replace the master cyl cap, after seeing that the brake fluid level is showing between the lines on the sight glass window. If not, add more brake fluid before installing the cap. Then install the master cyl cap. Tighten to being shut the brake caliper bleeder. Now rapidly and repeatedly fan the brake lever: squeeze, release; squeeze, release; repeat. You should feel the lever gets firm, and the point at which its travel stops is further from the handlebar. You bled your brakes.
