Do tou have the primer tank clamped to the outside og the chassis? Looks that way in the picture.
I removed te two plugs from the side of the primer tank and two -8 fittings screwed right in, I removed the straight 1/8 NPT to -4 fitting out of the bottom and installed a 1/8 NPT 90 -4 fitting on the bottom. On the -8 fitting I installed a -8 coupler.
I plumbed my tank into the return line to the tank so that it is always full after the first start of the day. The pump in this picture was replaced with a larger one as this one was not up to the task
I plumbed the primer line into the top of the distribution block. This is a test to see if it worked.