Yep, that rear brake can be a bitch. I used a speedbleeder on my Breva 750 and now use the suction tool (forgot the name). Without either one, that brake just doesn't want to bleed. And yes, the little black rubber piece just compresses back into the lid and flattens out. When you're bleeding the brake and you get good suction but run low on fluid in the line and bowl, the suction makes it pull out (stretch out) as it's being pulling by the suction on the other end of the line.