I'm not a well guy, but it sounds like a footvalve issue to me...

MTG

By footvalve, do you mean check valve? If so, that's brand
new...It's a brass valve, but the pvc one previous was
acting the same way...

You have a leak.

Most likely a coupling. We run into this all the time. The leak lets air in behind the check valve, killing the vaccuum that holds the water in the pipe. You were correct to change the check valve first. Now change all the fittings, couplings, and pipe.

I aggree with all above... and
well, it may seem like a silly thing to mention but... check the direction of flow on the check valve. Make sure it's not in backwards. It's probably ok or you wouldn't get ANY water but... crazier things do happen
Arthur