In the photo is that a 3 way valve at the bottom of the sight glass, Keith mentioned some about it but I didn't follow that either ... think I'm on an inactive brain week!
This is not for the schematic just explaining how it works
I always use one of these on top of my GL carbouy vent


this attatches to the meth in pipe
On the actual sight tube i swapped the bottom 90 for a "ball fix" 90 ,so it can be isolated
then directly above that 90 i put one of these,same type but a tee

with me so far?
So when the level is set,isolate sight tube with the ball fix valve
Attatch meth in pipe (which as we know sucks)
Flick pump on for a few secs
oil is sucked out
Geddit?