Nitrous plumbing A1A...??..

I put quick disconnect crimp connectors on my solenoids.
To purge and check your fuel solenoid simply unplug the Nitrous solenoid wires. Start your car, arm your system and activate it (I just press my WOT switch) and the extra fuel will either stall or bog down the engine. Do this at idle...
As far as plumbing, what size line are you running from your bottle?
Typical small kits use a -4an (which is what your previous inquiry of the N20 PSI gauge is spec’d out for).
Larger kits use a -6an line from the bottle to solenoid.