You have two chambers in the brake reservoir container. The rear one feeds the front brakes. There is a little dam between the two chambers. When you pour fluid into the reservoir, you have to fill it full enough to allow the fluid to overflow the dam and fill the second chamber. Sometimes it looks full and until you hold a light up to it, you can't really tell for sure. If you don't have both chambers full, then you won't get a good bleed and will always be sucking air.

Another problem could be old/bad rubber brake hoses that have collapsed inside. If they are over ten years old, think aobut changing them. There is a date of manufacture on them.

A pressure bleeder is the best way to do your brakes I think.

Len