#3 is right, you don't need a "T" fitting, it won't be running that long. I have never seen a "weak" pump, either they work or they don't. Running the engine with the line dumping into a bucket will tell me if I have a "healthy" stream of fuel or not.
I've seen plenty of weak pumps at least half a dozen over the years. Start and idle great, might even drive 20mph, etc but as speed goes up, .............................
And fuel pressure AND FUEL VOLUME is not just about the PUMPS either. It is the "end to end system" from the fuel sock in the tank, to junk in the tube, to bad hoses at the tank and pump inlet, and to air leaks into the hoses/ tubing. And plugged filters. And crimped tubing / hoses. And worn cam lobes
"Pump into a bucket." I admit this goes a LONG way. Many times if a pump produces volume, the pressure is not an issue
