I will probably need to re-prime my shallow well jet pump once again as I am moving it's location. The tiny opening of the pump prime is a pain when fiddling with the plug. I was thinking of plumbing this directly into the upstream system pressure line and maybe filling it from a 1/2" tee with a ball valve above the pump. Open the valve, fill the pump casing as well as the prime opening through the valve, close the valve and fire it up. What effect would this have when pump pressure is allowed into the prime port? Worse case, I guess, would be to add another 2-way valve just above the prime port so I could effectively shut it off before starting the pump. It would then act as the tiny plug does now but still allow me to fill the pump and prime easier.

The only question I have about that kind of setup is this. When you prime a pump, it's a water in and air out kind of thing. The line is filled with air which must be displaced with water. Your setup would put water in, but how would the air get out?

An alternative is to plumb in a 3/4" or 1" T into your suction line with a threaded cap on it. It will handle a lot more water more quickly than the small opening in the pump housing.

When I have primed in the past all the air went out the open faucets upstream and they would be closed, starting with the lowest ones first. I see what you mean, some of the air may be sucked back in through the prime port opening and I may lose my prime before I get the line to fill with water. I may just add a valve above the prime port with a larger pipe to aid in filling and close it to start the pump.