Brake bleeding help needed!

[cst350]

Trying to bleed the system for the first time with new SS lines. I have read alot of posts about the right way to do it. Heres the problem, The brass plunger on the front of the combination/proportioning valve will not go in. The manual says to depress it, but it wont. I even bought a new one thinking my old one was bad since it didn't go in either. I bench bled the master, and started bleeding at the drivers rear (actually further from the Master than the passengers side if you look at how long the brake lines are)

Anyone know if it needs to go in, or should I just make sure it doesn't come further out with a clamp. Been getting air from the rear lines all day and have gone through 1/2 gallon of dot3. Almost to the point of taking it to a shop... but I like to do as much as I can myself.

CST350