How to fix a fuel isolator if you mess it up

Don't do what I did..
This would be the fix it for it...

Once everything is removed, using 50/50 mix of anti-freeze & water, fill the gauge-side of the isolator.

Next, attach the line and fill the line, while stretching upward. Supply a vacuum source to the fuel-side of the isolator (such as from a vacuum pump), and continue to fill. Then with vacuum still applied, cap the end of the line with a male, -4an line cap.

Now, fill the back of the gauge through the fitting.

Mount the isolator (do not hook the fuel pressure line to it yet), and route the line going to the gauge, into the vehicle, to where the gauge is going to mount.

Again, supply vacuum to the fuel-side of the isolator, and while you are holding the gauge in one hand, and the line in the other hand, it works well to have an assistant uncap the line for you (removing the previously installed line cap). Then in one brief motion, hold the line against the fitting on the gauge, while your assistant tightens the line for you.

Now, you may release the vacuum from the isolator, and hook up the fuel pressure line.

You are now done.

Can you explain what the fuel isolator is, what it does, and where it is mounted?
Also, why you needed to fix the isolator?
Maybe a picture of what it looks like?