You don't have to tap into the high pressure fuel line for a test port, IMHO.
Here's what I did on my Honda.
Cut the low pressure return line. Install a male & female quick disconnect fitting. Prepare a matching disconnect fitting attached to a 6' piece of 1/4" clear gas resistant hose/tubing. Coil up and zip tie to the car somewhere soo it's handy.
In normal operation, the quick disconnects are connected and since they are in the return line, the pressure is virtually zero (or very, very, low). When it comes time for the sample, I disconnect the fittings (no tools required) and plug in my test hose fitting in the line that came from the regulator (not the line from the tank!). The other end goes in the sample jar, several feet away from the (hot) car. I turn the ignition off and on a couple of times to let the pump run until the sample is collected. When finished, I disconnect the test hose and reconnect the return line.
Some people put the fittings in the high pressure side. One can certainly do this since the fittings are rated for high 200psi. But I was more concerned about the Murphy aspect in having the fittings work loose and causing a problem. I am very comfortable with using the return line since there is no pressure!
The formula car guys do something very clever (and safe) as well. They put the quick disconnect fitting in the supply line to the fuel pump (another 'zero' pressure line). When they draw the sample, they disconnect from the pump and connect their test hose in its place, and then just blow into the fuel cell vent line to push fuel into the sample bottle. No electronics required!
The fittings are pretty cheap, ranging in the $20-$30 per fitting depending if it's male or female, and the type of hose connection (barbed for hose, SAE, etc).