I was trying to bleed the clutch line with my son pushing on the pedal and after a few mins I remembered reading about other people struggling to do it. We were using the same procedure as brake bleeding and progress was slow, then I saw it !!
As I opened the bleeder, the clutch lever sprung back, but of course the pedal in the car hadn't moved, so no fluid moving in the line, how could the spring jump back ??
A: by sucking air back in the bleed screw.  Hmmm - first thought was maybe the bleed tube needs to be full of fluid ? Nope.
Then I got it. the secret is to open the bleed valve before junior presses on the pedal, then when he does, he simply pushes  a stroke load of fluid out the line, close the bleeder, pull the pedal off the floor, open the bleeder, push the pedal, etc. The clutch never moves or opens at any time. Finished in 2 mins. All the old fluid flushed out, clutch point now higher off the floor. Yay! Secret is - don't try to use the traditional brake line procedure, ie don't push on the pedal before the bleeder is opened. 
 

Or do what I usually do and use a large syringe on the bleed nipple and just suck the new fluid through 😊

I guess that's a solution if you have noone helping to push on the pedal, must be a pain sliding in and out from under the car to check the reservoir level.

Vac bleed works a treat.