Sounds like the check ball is not seating. Mine did that. Take the spout off and look for dirt inside. Clean it with CLR to remove any calcium and see if it's better. You also may have a leak in the hose letting in air when you pump. It's easy and to change and they get pretty nasty over time. But be careful removing the hose from the tank as the spout can crack easily. Take a sharp knife and cut along the top of the hose parallel to the spout with just enough pressure to cut through the hose.
Also, I bought a tiny electric pump with push button switch and connected it in series with the hand pump. Now I can pump or push a button.
Funny story: When we were traveling something was bumping up and down on the switch. Lost half a tank of water haha. Note to self, disconnect the battery!