I feel like I can fix this assuming this tank is not a bladder. Also just noticed Water spits out of the valve stem located before the tank when I remove the cap. Maybe it’s a bad stem which is causing pressure loss or the check valve causing water to return to the well itself
Since you have no leak, the real cure might be to simply replace the
snifter valve. There is a nice search term for you .
The snifter valve is similar to a regular tire Schrader valve, but with a really weak spring. When there is a vacuum, air is sucked in. When there is no vacuum, the valve should close. Yours doesn't. The cap on a snifter valve is a special vented cap. It keeps crud out, but not air. Regular valve caps seal, and that is what somebody put on yours to work around the failed valve.
To work around this for now, try to get water out and more air in.
What I don't know is what is a 1/8 or a 1/4 inch snifter valve. I suspect that refers to the NPT thread, but I am
not sure. Here is a chart of NPT dimensions:
