What happens is the LSPV has 2 lines coming from the front of the truck, then one output to the rear axle. One of the lines from the front is there rear brake circuit, the far left line in the above photo. When the LSPV is doing it's job and reducing brake pressure to the rear brakes, it has to bleed the excess pressure off so it sends the excess pressure back up to the front brake circuit. That is the line you see connected to the left on the T. If @yotadude520 looks at that T on his truck now, he will see a plug in the T there, I just cut the end off the line, folded it over and soldered it shut. The rest of the line was never installed when I was putting the truck back together. So the rear circuit line just has a simple coupling above the rear axle then there's another piece of hard line that extends and connects to the hose for the rear axle.
Very simple.
Very simple.