It sounds like a captive air tank but no bladder. Open the valve (if there is one) at the bottom of the tank and completely drain it till empty. There should be an air volume control on your tank externally that is probably in need of replacement. A $10 item that might keep this problem from reoccurring with waterlogging.
Once you know the tank is completely empty, refill tank by normal process of running the pump.
If your tank waterlogs right away, you need to replace the tank for the reason it probably has a leak allowing the air to dissipate.
DUNBAR
Website Moderator