Well, let's try some things then. I'll refrain, from filthy fucking heathen and refer to you as filthy heathen, if you don't mind?
So, filthy heathen. On the inline, once filled and settled, it will be about 1/2 to 2/3 high on the inside of the inline chamber. Basically, if the water level is above the slits outside the inner perc tube and inside the tube... you're good.
Next, the tree. Hopefully, they're clean cuts and large enough. Fill the water level in the tree, about an 1/8" above the top cut.
Now, some dry runs. Practice with the piece and watch that tree (you're ignoring the inline, for now). If setup/made correctly, you should be able to pull light enough to fire, just the slits on the tree. Next to nothing should be firing out the bottom of the individual tubes. Notice how the feel of the pull changes, with the amount of suction you apply.
Also, that's not a lean back piece. I see that a lot of times, with guys kicking back with their vertical piece. You're doing next to nothing in that case, except making a nice piece of glass operate like @$&#.
It looks like a nice piece. If the cuts are good, then water level is what you need to deal with, filthy heathen.